Examining Regulatory Pathways That Enable and Constrain Urine Recycling

Abstract

Today’s linear nutrient flows are rooted in a long history of agronomic and wastewater engineering strategies that have created cascading environmental, social, and economic side effects, signaling the need for more holistic and circular approaches. Our examination of the regulatory pathways that enable and constrain urine recycling—an underutilized approach to repurposing human waste as fertilizer—addresses a persistent research gap related to the mainstreaming of transformative technologies. Framed around policy process theories—Street Level Bureaucracy and Multiple Streams Theory—our methods include a review and mapping of 54 regulatory documents; action research where we reflect on our own efforts to expand urine recycling; and interviews with 16 practitioners and regulators in four states which, to our knowledge, are the only places in the US with efforts to scale up urine recycling in community settings. Given its circular nature, a key challenge we find is a lack of clarity around which sectors, or what scales of government, “own” the decision to allow the collection and use of urine as a fertilizer. Working around these challenges, we show how practitioners use many practical strategies to simplify the approval process and reduce the risk aversion regulators face when confronted with ambiguous rulemaking.

1. Introduction

Today’s linear nutrient flows are rooted in a long history of agronomic and engineering strategies that shaped industrial agriculture and the way societies manage human waste [1,2]. These technical fixes, however, have resulted in cascading environmental, social, and economic side effects, signaling the need for more holistic and circular approaches [3,4]. We examine one possible solution: urine recycling, which involves “urine diversion” (the collection of urine) and the production and use of “urine-derived fertilizer” (UDF; the end product of treated urine). This approach to repurposing human waste for use as fertilizer has a long history [5,6], but is underutilized today, particularly in the United States (US) [7]. Urine recycling could revolutionize wastewater treatment systems that are aging, overburdened, costly, energy-intensive, and inefficient at recovering nutrients; lower dependence on concentrated and unreliable global fertilizer supply chains; and reduce associated greenhouse gas emissions and water pollution [3,4,8].

As urine recycling pilot projects have expanded over the last two decades, particularly across Europe and the Global South [9] (see Table S1 in the Supplementary Files [10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28]), research has also accelerated to analyze the nutrient makeup of urine—showing that urine contains 70% to 80% of the nitrogen (N) and 50% to 70% of the phosphorous (P) found in sewage [29]; design urine diverting toilets [30,31]; develop treatment techniques for removing pathogens, pharmaceuticals, and toxins [32,33,34,35,36]; compare the costs, energy use, and environmental impacts of urine recycling and conventional wastewater treatment [37,38,39,40]; produce liquid and solid forms of UDF [41,42]; model the potential of UDF to offset global demand for N and reduce greenhouse gas emissions caused by synthetic fertilizer [4,43]; and examine factors influencing public and farmer adoption of UDF-grown food [44,45].

Research to date, however, says less about the policy environments that enable or restrict the adoption of urine recycling. Policy guides in the grey literature outline the types of regulations that are needed to enable urine recycling projects, such as WHO’s series on “Guidelines for the safe use of wastewater, excreta and greywater” [46] and a report issued by the Eastern and Southern Africa Water and Sanitation Regulators Association [47]. Academic researchers have also carried out desk reviews of regulations that restrict wastewater reuse, such as in Portugal [48] and the US [49]. In one such analysis, Merck et al. conclude that, “Even if other social and economic concerns are addressed, it is unlikely that urine diversion can be scaled up beyond the pilot or trial stage if innovators do not attend to these regulatory regimes” [49] (p. 6).

As Merck et al. [49] suggest, what remains to be studied are the impacts of these regulatory regimes on urine recycling systems on the ground, from the perspective of practitioners and regulators doing the work. The limited research that exists along these lines focuses on the Global South, such as Ekane et al.’s 2014 review of circular sanitation projects in sub-Sahara Africa [50]. Despite finding many “toilet to farm” (p. 249) pilot projects, they described how these systems were not able to scale up due to perceived risks, sunk costs, and “polycentric governance” (p. 251), where regulations and the delivery of sanitation systems is divided across ministries of health, water, environment, and education as well as district and lower-level governments. Similarly, in their analysis of options for nutrient recovery from sanitation systems in South and Southeast Asia, Bekchanov and Evia [51] argue that there are “disputes over conflicting interests” (p. 29) among ministries of urban development, finance, communication, and agriculture regarding the financing of new sanitation infrastructure, management of public awareness campaigns, and standards for the use of UDF and other organic fertilizers.

Taken together, the existing research does not consider the strategies that practitioners have attempted to secure permits or change policy to establish urine recycling projects, nor the ways that regulators have responded. This reflects a persistent research gap in the environmental policy literature related to “practical policymaking”—knowledge needed about the day-to-day work it takes to create enabling policy for transformative technologies to become mainstream [52] (p. 33). Our research seeks to close this research gap by asking: what regulatory hurdles currently exist and what are the pathways for establishing urine recycling? We selected the US as our point of focus given the relative lack of urine recycling initiatives [49] and its potential environmental and associated benefits, outlined below.

Background: The Potential Growth of Urine Recycling in the United States

Establishing urine recycling in the US could address multiple challenges related to the country’s dominant fertilizer and wastewater practices. The production and overuse of N and P fertilizers—on farms as well as lawns, landscaping, and turf—are major drivers of the country’s greenhouse gas emissions and dead zones in oceans and lakes that impact drinking water, recreation, and the health of aquatic ecosystems [53,54]. For the last five years, farmers in the US have also faced shortages and price hikes in synthetic N fertilizers as a result of the COVID-19 pandemic, the Ukraine war, extreme weather events, and natural gas price fluctuations [55,56]. Scholars also debate whether the demand for mined P fertilizer is outpacing supply, nearing “peak phosphorus” [57], or whether access is at risk, with 70% of known global P reserves managed by Morocco alone [58,59].

Outdated and inefficient wastewater infrastructure in the US further contributes to greenhouse gas emissions, harmful algal blooms, and eutrophication [8]. Many wastewater facilities recapture some nutrients as biosolids [60]—treated sewage sludge applied to more than half of arable land in the US [61]. However, after decades of improvements to energy-intensive technologies, treatment plants on average recover only 11% of N and 21% of P from sewage sludge [8]. The remaining N and P is released into waterways, landfilled, or lost as gases, N₂ (innocuous), and nitrous oxide (a potent greenhouse gas) [62].

Current approaches to wastewater infrastructure may also be exacerbating an affordable housing crisis. A quarter of households in the US rely on septic systems that often fail with age and were not designed to remove most nutrients [63], leaching additional N and P into aquatic ecosystems [64]. Many low-income rural homeowners cannot afford to meet costly, updated septic system requirements [65], while increasingly stringent wastewater treatment standards threaten to bankrupt historically underserved municipalities that cannot afford to build or update centralized wastewater treatment systems [18,66]. In some places, such as New York City, new housing construction is also facing delays as aging treatment facilities reach capacity, unable to process more N [67].

2. Methods

To obtain a holistic view of the regulatory process related to urine recycling, we triangulated three forms of qualitative data: document review, action research, and targeted interviews. Qualitative research helps reveal contextual factors, individual experiences, perceptions, and human interactions that can explain outcomes, offering insights on social phenomena not typically apparent in quantitative studies [68].

We focused on four states which, to our knowledge, are the only places in the US with initiatives attempting to scale up urine recycling in community settings and that have urine-derived fertilizer products registered with their respective state agricultural authorities. This includes initiatives in the following:

• Massachusetts (through the Massachusetts Alternative Septic System Test Center which is piloting urine diverting toilets in Falmouth and is trying to expand these systems throughout Cape Cod and surrounding islands);
• Michigan (where our team since May of 2024 began exploring the possibility of establishing a test bed for urine recycling off-campus—the basis of much of our action research);
• Oregon (at the building scale for office and retail space in the PAE Building in Portland as well as a portable toilet company that is no longer in operation);
• Vermont (led by the non-profit Rich Earth Institute, which collects urine from nearly 250 residents and carries out agricultural research on 9 farms. Rich Earth’s commercial spin-off, Brightwater Tools (Brattleboro, VT, USA) and Wasted (Williston, VT, USA), a portable toilet company also operate in Vermont).

For our document review, we collected any codes, standards, laws, and administrative rules that shape permitting requirements at the state and national level that could enable or restrict urine recycling related to plumbing, wastewater processing and transport, and fertilizer use. The text of laws and administrative rules is publicly available through the internet. Standards and codes were accessed using interlibrary loan or via purchase (Tables S2 and S3 in the Supplementary Files list the does and documents reviewed [69,70,71,72,73,74,75,76,77], and Table S4 provides a glossary of the institutions and codes referenced in our regulatory maps and elsewhere in the paper).

For the action research portion of our study—a method where researchers engage in and reflect on action intended to bring about a change [78]—we began by attempting to expand urine recycling beyond the confines of a small urine recycling project that has existed on the campus of the University of Michigan since 2017. This included reviewing Michigan’s existing wastewater and fertilizer regulations (part of our larger document review, described below) and interviews we carried out with local and state regulators (see below) to determine how to secure a state-level agricultural fertilizer label to use UDF in agricultural trials. Through this process, we also decided to work at the national level on two fronts. On the advice of the Michigan Department of Agriculture and Rural Development, we began engaging the Association of American Plant Food Control Officials (AAPFCO), whose guidance forms minimum national standards for fertilizers [79]. One team member, Lippincott, also advocated for changing both major model plumbing codes for North America, successfully adding urine diversion to one, the International Plumbing Code (IPC) [80]. Leveraging the authors’ action research on permitting of UDF in Michigan and engagement with AAPFCO, we also offered technical assistance to the Rich Earth Institute and Brightwater Tools regarding their efforts to permit UDF as a fertilizer in Massachusetts, New Hampshire, and Vermont.

We also identified 16 urine recycling key informants to interview. Co-authors Love and Lippincott—who have 15 or more years of experience working on wastewater nutrient recovery in the US—first suggested practitioners they were aware of that have been leading urine recycling efforts in Massachusetts, Oregon, and Vermont. We then used snowball sampling, asking initial interviewees to share contacts of other practitioners or regulators they worked with to secure permits. In Michigan, we began by inquiring in our local health department about how to establish a urine recycling project in a community setting. Initial contacts then suggested other regulators to meet with at county and state levels.

Seven interviewees were practitioners who had each been working to establish and scale up urine recycling for over a decade in Massachusetts, Oregon, and Vermont. Nine were regulatory staff: one each at the state level from Massachusetts, Oregon, and Vermont in wastewater/environmental agencies who provided the urine recycling permits in those states. Six regulators were from Michigan—three at the state level agricultural agency and three in county public health offices who helped us learn about Michigan’s wastewater and fertilizer regulatory environment and guided our state-level agricultural fertilizer certification process.

Interviews (Informed consent for participation was obtained from all subjects involved in the study. This research was approved by the University of Michigan Institutional Review Board (HUM00234738) on 16 May 2023.) were conducted by two or more members of our research team over Zoom for an average of 45 min and were recorded and transcribed. Some interviews involved two participants from the same state simultaneously. The interviews were semi-structured, an approach that uses pre-established questions and follow-ups to ask participants to expand and explain why or how they approached their work [81]. All interviewees were first asked to describe their career path and how they came to work on urine recycling, wastewater management, and/or fertilizer permitting. We then asked practitioners to describe how they approached regulatory officials to gain approval to collect and process urine and distribute UDF. We discussed challenges they faced and strategies or factors that supported their ability to secure a permit. Regulators were asked to first describe the steps that were taken (or that our team would need to follow, in Michigan) to permit urine recycling systems in their state. We also asked how the end product of urine recycling—UDF—was (or would be) categorized in their state for use as a fertilizer and about the extent to which local and state regulators and agricultural, public health, and environmental regulators have differing perceptions or overlapping regulatory jurisdictions that affect urine recycling.

Outside of what we learned in documents and interviews regarding the permitting of UDF as a fertilizer, research about the market demand and farmer adoption of the end product—UDF—and customer acceptance of products fertilized with UDF was beyond the scope of our study. Other research to date has shown that public and farmer perceptions of UDF-grown food is generally positive, though the use of urine on non-food crops, and in landscaping and horticulture, is often viewed more favorably [44,45,82].

Theoretical Frame and Analysis

The analysis of our three data collection methods was iterative, as we compared and triangulated key findings that emerged, framed by two policy process theories. From the perspective of regulators, we draw on the theory of Street-Level Bureaucracy, which posits that front-line staff have considerable discretion to interpret and enforce rulemaking, particularly when established rules are ambiguous [83]. Researchers who have applied this theory tend to assume there is a “correct” way to implement policy and that bureaucrats often misuse their discretion to not comply with the policy’s intent [84]. Applying Street-Level Bureaucracy to the case of urine recycling raises new questions about the way that decision-makers intervene when the regulations around a technology or new practice—like collecting, processing, and applying urine as a fertilizer—has never been done before in a particular locality.

We also employed Multiple Streams Theory [85] to examine how practitioners advocated for changes in policies to support urine recycling. This theory suggests that several elements must converge to create an opportune moment for policy to change—a “policy window”—when there is a growing understanding of the problem (the “problem stream”), viable solutions exist (the “policy stream”), and key decision-makers are motivated to act (the “political stream”) [85,86]. These windows of opportunity often occur when there is a “focusing event” [87], such as a disaster or change in leadership that advocates take advantage of to advance their cause. Such windows can also be intentionally created by policy “entrepreneurs” or “champions” who have access to decision-makers and can spur them to act [88]. Also called “boundary spanners,” such individuals are adept at translating the goals, organizational cultures, and language of bureaucracies [89] to coordinate and build trust between agencies and outside groups and advance innovative solutions [90]. These are skills we expect to be important for gaining regulatory support for urine recycling across multiple sectors, including departments of agriculture, natural resources, and public health.

Drawing on these two theories to examine our data, we applied Fereday and Muir-Cochrane’s [91] approach to thematic content analysis to examine our interviews, using deductive analysis (based on themes from Street-Level Bureaucracy and Multiple Streams Theory) as well as inductive analysis (where we allowed other themes to emerge related to challenges and facilitating factors practitioners and regulators faced as they attempted to establish urine recycling projects). We reflected on our action research using prospective policy analysis [92], a process for documenting policy processes as they unfold, including the associated actors, interactions, and factors that emerge to shape the process. Our document review focused on visually mapping all the possible regulatory steps, codes, and rule-making bodies that practitioners in the US may encounter as they attempt to establish urine recycling projects, compared against the experience of interviewees and our action research.

3. Results

As we describe below, having few precedents has created considerable delays and confusion around how to regulate the various components of urine recycling in the four states we studied, but practitioners have also learned how to productively work with regulators to navigate the various agencies and permitting processes. Two regulatory pathways have emerged for managing urine diverting toilets: state-level approvals from departments of environment that are concerned with groundwater contamination (e.g., Vermont and Oregon) and a more fragmented approach in places where the authority for implementing sanitation systems rests at the local level, usually by municipal public health departments (e.g., Michigan and Massachusetts).

Authorizing the output of urine recycling—the use of UDF as a permitted fertilizer—has so far been managed at the state level, though using different mechanisms. The Vermont Department of Environmental Conservation first permitted UDF by writing a novel wastewater residuals permit to the Rich Earth Institute in 2017 (Residuals in wastewater refers to nutrients that are removed from wastewater in a solid, semi-solid, or liquid state, which are either sent to landfills, incinerated, or applied to (agricultural) land as fertilizer [93]; the permit was “novel” in the sense that the Department of Environmental Conservation had not developed this type of permit previously). In July of 2025, the Vermont Agency of Agriculture, Food, and Markets issued fertilizer licenses to the Rich Earth Institute and Brightwater Tools for their pasteurized and concentrated urine UDF products [94]. The Oregon Department of Environmental Quality issued a wastewater treatment facility permit to the PAE Building in 2021 [95] that classifies UDF as a fertilizer to be regulated by the Oregon Department of Agriculture [96,97]. The Michigan Department of Agriculture and Rural Development issued a specialty fertilizer permit to the University of Michigan in 2024 for research purposes [98]. The Massachusetts Department of Agricultural Resources (MDAR) issued a one-time permit to apply UDF as a fertilizer in 2017; however, the question of whether UDF should be regulated as a residual product of wastewater or as a fertilizer remains a matter of contention, with ongoing conversations among UDF advocates, MDAR, and the Massachusetts Department of Environmental Protection. Although not fully resolved, in June 2025, MDAR issued fertilizer licenses for pasteurized urine and a concentrate [42].

3.1. Mapping the Multi-Layered Regulatory Pathways

Similar to Merck et al.’s description of “regulatory regimes” that govern urine recycling in the US [49], the following figures outline the permitting that has been required in the cases our team studied. The figures depict the regulatory approvals needed along each of the urine recycling steps, starting with following appropriate plumbing codes and ending with permits needed to apply UDF on agricultural fields or landscaping, as well as the various agencies from federal to local levels involved in approving, inspecting, and implementing each of these steps along the way.

Figure 1 outlines the points where policy in the US affects urine recycling systems (noted in teal, e.g., at the point of transporting urine, selling UDF, etc.), and the permits, licenses, standards, and agreements needed at each of those points (in blue). Most urine recycling systems will only need to clear a handful of these policy hurdles; Figure 2 shows the minimum—and simplest—set of policy solutions likely needed to establish urine recycling to fertilize non-food crops. Each policy point is described in more detail below the figures.

3.1.1. Building and Occupancy Permits

To install urine diversion plumbing, an occupancy permit is required, contingent on both plan approval and successful plumbing inspection. Plans must be in compliance with local plumbing codes or require a variance at the discretion of building authorities. Currently, no local plumbing codes include urine diversion; however, the optional ANSI/IAPMO (American National Standards Institute/International Association of Plumbing and Mechanical Officials) Water Efficiency Standard (WE Stand) has included urine diversion since 2017, and based on our team’s proposal, the IPC committee recently supported the addition of a urine diversion appendix to the 2027 IPC. Code appendices and efficiency standards are a recent response to the need for energy and water efficiency, largely arising since 2010 [99]. Such codes are optional and not designed for direct adoption by jurisdictions. However, meeting the standards of these optional codes dramatically improves the chances of receiving a variance.

3.1.2. Toilet Fixture Certification

To comply with plumbing codes, urine diverting toilet fixtures must be certified to a commercial product standard that guarantees their function and load bearing capacity, which must be developed by a non-profit standards body compliant with the ANSI consensus process [80,100]. The current US standard is not designed to accommodate urine diverting toilets [101], and no fixtures (available in the US) currently meet this standard.

3.1.3. Shared Infrastructure Agreement

A shared infrastructure agreement, while not required, allows multiple private systems to share infrastructure and maintenance services. Such agreements are useful for ensuring proper operations and maintenance and lowers the cost of urine diversion systems. Various shared infrastructure and shared maintenance programs are recommended by the US Environmental Protection Agency (EPA) as the best practice for onsite system management [102].

3.1.4. Collection and Storage

Collection and storage of raw urine can be either private and exclusive to a building or a part of a private or public shared infrastructure agreement. Most septic regulation requires building owners to conduct regular servicing; however, such requirements are difficult to enforce, with negative consequences for human and environmental health [103]. Publicly shared infrastructure agreements and collection programs, such as the septic service district in Otter Tail Lake, Minnesota, are considered best practices by the EPA [102].

3.1.5. Hauler’s License

The vehicles and service providers hauling unprocessed urine will require tanks that meet transport requirements, vehicle and operator licensing, bonding, and insurance, just as septic hauling currently requires. Septic standards could be applied, but there is a risk of regulatory spillover, where requiring a septage hauler license could lead to urine being classified as septage (sewage solids and liquid). Our Vermont interviewees noted that the state requires septage hauler licensing for urine haulers, but has not categorized urine as septage. No other state has resolved transportation licensing for urine; however, Rich Earth Institute and Wasted have obtained septage licenses in Massachusetts and New Hampshire to support their processing operations in Vermont. If raw urine or treated urine is licensed as a fertilizer, it can be transported following state fertilizer transportation standards.

3.1.6. Treatment System License

Urine must be subject to public health controls appropriate to the urine’s use, ensuring disease transmission risks are minimized. Whether or not the applied controls are based on the specific risks posed by urine depends on the classification of urine by authorities.

3.1.7. Fertilizer Permit

For urine to be sold as a fertilizer, licensing as a fertilizer is required at the state level. Fertilizer regulators from every US state and territory and Canada coordinate through AAPFCO [79].

3.1.8. Nutrient Management Plan

The timing, rate, and methods for applying fertilizer, urine-based or synthetic, may be subject to best management practices for soil nutrient management, typically established and managed at the state level and conforming to Natural Resources Conservation Service Standard 590 [104].

3.1.9. Fertilizer Labeling Strategy

Communicating with growers and consumers about UDF, its regulation, benefits, and risks is crucial to the success of urine recycling [44,45,82]. Restrictions around UDF labeling and use will depend on urine’s classifications and provisions based on fertilizer standards established by both federal acts (e.g., the Food Safety Modernization Act), industry groups (APPFCO) and state agriculture departments. Whether UDF can achieve value-added labels such as “organic” may also affect adoption, according to our interviewees.

While all of the steps shown in Figure 1 may be required to establish a urine recycling system, our document review and interviews suggest that three regulatory processes form the greatest barriers to adoption, signaling the minimum requirements that any urine recycling project will need to manage: plumbing codes that limit installation and occupancy permits; treatment system licensing; and the licensing of the treatment systems’ outputs (see Figure 2). For current urine recycling projects in large buildings that produce fertilizer on-site, only the occupancy and treatment systems policy points must be addressed to begin operations. Additionally, our research suggests that licensing, use, and public acceptance of UDF are simplified by focusing on non-food uses, such as landscaping.

At all stages of the regulatory interactions, two questions emerge from our document review and interviews: can a urine diversion system be legally installed, and how will the system’s output be regulated? The answers to these questions have downstream consequences for the willingness of developers to install urine diverting toilets, the marketability of UDF, and therefore the economics of urine recycling.

As we found, plumbing codes must allow the option to install urine diversion systems in buildings and homes without requesting a variance. Figure 3 shows the path to code reform from the creation of code language at the level of standards-setting organizations; integration of codes into optional “reach” codes (codes that exceed minimum standards set by the state); adoption in primary code standards; secondary code standards (required in some instances); and finally, local and state adoption, interpretation, and enforcement. Because the US is split into roughly two plumbing code jurisdictions, two different paths must be addressed to achieve national standardization, depending on whether IAPMO or International Code Council (ICC) codes are adopted. These two code bodies have copyrighted their codes, which are updated on three-year cycles, making (quick) adoption of a single, national standard challenging.

Urine diversion would first have to be adopted into the appendices of the IPC and UPC (Uniform Plumbing Code) (Based on a proposal submitted by co-author Lippincott, an IPC Committee Action Hearing in 2024 resulted in a proposal to add urine diversion to an IPC appendix. The proposed change is now undergoing a public comment period and will undergo a final round of governmental voting, Validation Committee certification and ICC Board confirmation. The UPC Technical Committee rejected a similar proposal (Item 350) that would have added the WE Stand language for composting and urine diverting toilet systems to a UPC Appendix. This proposal was submitted by Pat Lando of Recode in 2024 and modified based on comments made by co-author Lippincott and Pat Lando in 2025) to make it eligible for adoption into the primary chapters of the reference standards, which, at the earliest, would occur during the 2030 and 2033 code cycles, respectively. State code adoption usually lags behind these national reference standards by two to six years, making 2031 the earliest possible date (The first draft of the language of these reference standards was created through the Recode Model Code process in 2014 by co-author Lippincott who served as code writer and lead editor. The Recode Model Code was approved for inclusion in the IAPMO WE Stand optional reach code in 2015, first published in the 2017 WE Stand, and first adopted by a state through the Oregon Residential Reach Code in 2021 [105]. We consider 2031, 17 years after initiating the code reform process, to be an extremely optimistic date for full adoption of urine diversion in any state plumbing code.) when variances will not be required for urine diversion. Until urine diversion is fully integrated into these standard codes, adoption will depend on variances issued by plumbing inspectors.

In our discussions and document review, we also found that categorization of a urine recycling system’s output will determine the marketability of UDF—including whether it can be called “fertilizer”—and the regulatory steps required to install and operate a urine recycling system. Figure 4 shows existing wastewater programs from the federal to state level that may be used to categorize UDF as a fertilizer and recognize urine recycling as a means of controlling nutrient discharges to waterways.

At the highest level, the EPA enforces the Safe Drinking Water Act, which governs the Underground Injection Control program supervising large onsite septic systems (~20+ users). The EPA also enforces the Clean Water Act, which governs four programs: (1) the National Pollution Discharge Elimination System which tracks the state-level permitting of wastewater treatment facilities and stormwater discharges; (2) solid waste reuse; (3) biosolids and other residuals associated with wastewater systems; and (4) Total Maximum Daily Loading (TMDL), which establishes locally-specific mass discharge limits for pollutants that a waterbody can withstand and still be “fit for purpose” such as recreation, drinking, etc. TMDLs affect the total amount of N, P, and other nutrients centralized wastewater systems (and other point and non-point sources) can discharge into rivers and lakes. Additionally, EPA regulates and assists state waste disposal and recycling programs through the Resource Conservation and Recovery Act. The US Department of Agriculture (USDA) also offers guidelines for fertilizer use, which must also comply with the Clean Water Act; however, USDA fertilizer guidance is not binding on states. Across all these federal standards, state-level agencies can set stricter standards than those established at the federal level and exercise discretion in program implementation. State-level agencies must also contend with the overlapping jurisdictions and common goals of these federally mandated programs.

3.2. Options and Tradeoffs for Categorizing the Output of Urine Treatment (UDF) as a Fertilizer

Eight interviewees noted that there are various implications for marketing the outputs of urine treatment (i.e., UDF) as a fertilizer depending on the way UDF is categorized by either federal or state regulatory rulemaking processes. It seems unlikely that federal rulemaking will determine a universal fertilizer certification system for UDF, particularly in the short term given that rulemaking around more nationally pressing, related concerns, such as revising the biosolids rules, is unlikely [106]. It can therefore be assumed that state processes will categorize urine, as has so far been the case the four states we studied. We found that state agencies can define UDF as one of three products: wastewater for non-potable reuse; a biosolid that can be treated and licensed as a fertilizer [107]; or a secondary material for beneficial reuse as a fertilizer or soil amendment under a solid waste management program [108].

At a surface level, wastewater appears like an obvious fit for urine, a product usually flushed down the toilet. However, if urine is to be reused as wastewater, it will have to conform to state non-potable reuse standards that often limit the nutrient concentration of reclaimed wastewater [109]. Since most states do not have non-potable reuse programs, and those that do often limit nutrients, categorizing urine as wastewater will only ever be a regionally specific option. There is also no clear regulatory path from classifying urine as wastewater to marketing UDF as a fertilizer.

Because biosolids regulations give regulators robust oversight of contaminants and a suite of treatment options for urine designed to destroy viruses and bacteria, seeking a biosolids classification for urine is a common suggestion of regulatory staff. However, urine is substantially different from biosolids in its origins, risks, and composition. Biosolids are solid or semisolid residues of wastewater treatment that are mostly organic carbon and carry both a disease risk and capture contaminants from a wide variety of domestic and industrial sources [46]. Increasingly, state-level legislation is adding restrictions to biosolids, including a total ban in the state of Maine [110]. Additionally, the AAPFCO definitions state that the use for fertilizers does not allow for liquid biosolids [111], limiting the ability of biosolids-regulated urine to be sold as fertilizer.

Alternatively, urine can be categorized as a secondary material through a solid waste beneficial use program that seeks to find valuable uses for non-hazardous domestic and industrial waste products [112]. These products are wide ranging, from coal ash and metal casting sands to the dirt washed off of vegetables at food processing plants. The Rich Earth Institute permit for UDF in Vermont is through the Vermont Department of Conservation’s Waste Management and Prevention Division, which created a special category for urine (EQ Urine), applying relevant biosolids treatment and testing requirements while waving others [113]. Although it may be strange to think of urine as a “solid waste,” this program would potentially offer the most direct route to licensing urine as a fertilizer. However, as four interviewees noted, the process of drafting a custom permit with specific handling, treatment, and testing requirements specific to urine requires motivated staff willing to put in the effort, making staff discretion and agency capacity the most challenging factor of this approach.

3.3. Falling Through the Governance Gaps: Confusion Caused by Having No Regulatory Home

Given the numerous agencies and permits that urine recycling advocates must navigate, it is no wonder that trying to secure the necessary approvals can be complicated. Our interviews and our team’s experience demonstrate that one of the major challenges with getting approvals for urine recycling is the lack of clarity around the rules or agencies that should establish permitting. As one practitioner put it, “I think that regulators often don’t have clear guidelines because the material that we’re talking about [i.e., urine] isn’t defined in the rules that they’re looking at.” This creates multiple points of confusion and governance gaps practitioners must negotiate with little guidance.

In some cases, the issue is a matter of scale, where regulators try to enforce industrial-scale practices on household or community-level urine recycling projects. However, as one practitioner explained, this means that: “all these kinds of categories for these large facilities don’t really make sense or apply for us.” In other cases, state agencies try to apply tangentially related regulations that they manage, but that are ultimately not appropriate either. As another practitioner described: “The issue that we’re running into…is that the only rules they have to apply in this case…are the onsite wastewater rules, groundwater discharge rules and water reclamation rules. …They’re undecided on how they can find a pathway through their own rules for [urine recycling] to happen.”

With no guides available and little communication between staff who might need to issue different permits—even in the same agency—it can take time for urine recycling practitioners to identify the permits they need. Staff at one organization began collecting urine and working with farmers who were applying UDF after securing permits from the state department of environment for urine treatment and land application. As the project grew, they were unaware that another program in the same state agency would also need to permit the new plumbing and storage systems they were installing, which forced them to “bring all of these things into compliance and a few years of a lot of frustration.”

In two other locations, practitioners were “booted around” multiple times. In one case, a urine recycling project landed in a department that was willing to manage the permitting process, but in the second case, a state regulator at a department of environment explained how the permit one practitioner was trying to secure was moved back and forth between different staff. They explained, “I think [they were] trying to get people in regulatory positions to make a decision where they’re not really sure: Is it up to me? Do I own this decision? …Nobody knows who says yes or no. So everyone was just like, ‘well, I don’t know.’ And it just went in circles until it petered out.”

The fact that urine recycling is inherently part of a circular system—and therefore crosses sectors that are often in different units of government that manage drinking water, wastewater, and agriculture—also complicates the matter, as one practitioner explained:

“I think there’s a gap between each of those jurisdictions of regulators not really knowing where it sits because it’s part of a cycle instead of part of a line. In a line, it’s very easy to hand off one thing to the next department, and it’s easier to draw clear boundaries between, is it a waste or is it a fertilizer? I think that then kind of causes its own cycles of regulators who pass off questions about how to permit a urine recycling project back and forth to each other because they don’t know where it belongs.”

In Michigan, we also went back and forth to determine which government staff to talk with initially. Because many regulators knew little about urine recycling, our meetings with them became more of a two-way conversation as opposed to one-way interviews, where we answered their questions and shared available research on the nutrient content of urine, treatment techniques, and its use as a fertilizer. Our conversations revealed that public health and environmental staff would be more likely to give us the necessary approvals for a community-scaled urine recycling project, and see it as posing less risk, if our state department of agriculture first recognized UDF as a legitimate fertilizer. This set us on a path to first obtain a fertilizer permit—for the end product—which we expect will ease future approvals for the urine collection, transport, and processing sides of our project when we are ready to expand.

Practitioners in another location got around this cross-agency, multi-permit complexity in another way. They initially tried to meet one-on-one with various regulators to establish the “handshakes that had to happen from city to county to state…[but] people were getting really frustrated, because there were all of these questions circulating… We had to get everybody in the same room to find out where the gaps were… It was like, ‘Okay, we’re locking the door, we’re going to have a discussion.” The symposium they held helped them “find out who is really in charge, and what permits needed to be pulled” and to collectively problem solve. As one person explained: “Some of these regulators were pretty creative. They’re like, if we call it this, then we could do it this way… [And we would] kind of challenge them with, how would you permit this?… Then they started to be solution oriented rather than just saying, ‘No, no, no’.” Another person went on to describe how:

“It was everyone that was going to touch a drop of water, from the fire marshal, to the plumbing inspector, and [others from the] state, city, county—everyone was in the room, so that there was no finger pointing. We presented goals we want, systems we’re thinking about, and we left that room with two permits that needed to happen, and a point person for each permit. There was clarity on what we needed to do and everyone knew their role and the permit that was needed. It kind of demystified a lot for everyone.”

In addition to the lag time between code changes made by national standards setting organizations and code adoption at the state level, the division of regulatory responsibility across state and local levels can also create challenges, particularly when local governments have considerable autonomy over plumbing and wastewater systems. In one state, a urine recycling organization was making progress in towns where local public health departments and plumbing boards were becoming familiar with urine diverting toilets, but when they approached state regulators who were not familiar with these systems, they delayed the process. One practitioner described in detail a particular case where:

“The homeowner went to the building department and went to the plumbing inspector and said, hey, I want to install a [brand of urine diverting toilet]. And they said, “oh, yeah, I know that system. I’ve seen it. …Just pull a plumbing permit as normal and you don’t need any special variances or anything out of the ordinary.” …And then when he went to the town [government], they were familiar with the system, and they said, “Oh, yes, we’re aware of that, and here’s the way to do it.” So they signed off on the installation. Now, if you were to approach the state wastewater officials and say, “can we use this system?”… They would probably say either “no” or, “well, that’s going to require a pilot permit with all kinds of engineering and testing and sampling for, like, two years afterwards.” So there’s this huge disconnect with what the state officials are actually aware of [and] what’s out there and [already] permitted by their local authorities.”

3.4. Regulatory Staff Discretion: Erring on the Side of Risk Aversion

Particularly because urine recycling has no clear regulatory home, practitioners acknowledged that there is no incentive—and in most cases, a disincentive—for a regulator to offer a urine recycling permit. As one practitioner noted, “nothing in their job requires them to say ‘yes,’; they get no reward from taking risks. They can continue a paycheck and less stress if they say ‘no.’” This practitioner believed that if a regulator is unable to see the benefit—a positive “legacy” they can establish by allowing an uncertain innovation to move forward—it is easier to stay with the status quo. Another practitioner reinforced this notion, indicating that:

“Regulators are trained to think about worst case scenarios in a way that I think is really useful, because as a citizen who exists in a community where industry is happening…it makes me feel good that someone at the government level has thought about, “How could this go wrong?” …[But] sometimes that has been frustrating because I feel like the worst thing that could happen, given what I’m proposing, wouldn’t have really big public health outcomes in terms of just using urine in this particular context. I think that there is a public health aspect to it, but sometimes that [risk aversion] can get in the way of thinking about…the consequences versus benefits. There is a bias in the system towards [thinking that] any risk means that you probably can’t do it or [assuming] there’s going to be a ton of hoops to go through.”

Similarly, one practitioner who struggled to secure approvals felt that regulators were driven by “emotions” rather than evidence. They also felt like staff who were about to retire were stalling:

“I felt continuously [that] decisions were being made upon dated language—old codes in old books and often not allowing room for science to be part of the conversation, driven by emotion… Too many of those individuals within those spaces are often so extremely cautious, which is maybe why they like to work in those spaces and would rather not think about things from a creativity standpoint… And I think [a state regulator] was also on the verge of retiring. So …the attitude was “it’s going to be easier to say ‘no’; it’s going to be easier to wait you out until we retire than to say ‘yes’ and run that risk”.”

3.5. Building Trust and Problem-Solving

The fact that rulemaking, and enforcement, can be fluid and open to interpretation, reliant on the discretion of decision-makers, also worked in advocates’ favor when they could find regulators who were interested in learning more about urine recycling and were willing to find a way to make projects work. As one state regulator explained, “I think rules and a lot of things in life are seldom a one and done thing. It’s a journey, [in] that ideally everyone learns more. You start seeing like, OK, where can we go? Does this still make sense? And how do we address it if it doesn’t make sense now?”

Four interviewees noted that regulators can also change their mind depending on who is asking or how they asked for approval. One state regulator described how they were more willing to work with practitioners who were responsive and proactive, showing an attempt to compromise:

“The more that you interact with the regulator community, the more you realize when to wear your—we would call it “white hat” or “black hat”… I generally joke that I’m wearing a “gray hat” all the time. Because I’m a regulator, I can’t unsee certain things …the flip side of that is being very cognizant of how many resources it takes to involve an enforcement process. Over time you tend to see what level things rise to. Can you take care of it yourself before you need to put on that black hat? How far do you let it go before you need to bring in enforcement support? …If you can get people to do things that they’re supposed to do without hitting them over the head, then that’s good for everybody… Most of the time as long as you ask for help and you don’t ignore us, or if you respond and say, “I need more time,” or “can we set up a compromise?”… [then we’ll work with you]. But when you just disregard repeated efforts by us to help you, at a certain point, you get dumped into the black hat bin.”

This regulator’s perspective is similar to one practitioner’s view that most regulators ultimately, “want to be part of the solution, even if their hands are tied. They’re used to people trying to squeak by with just barely legal—but we want to go beyond that and do even better than what is legal.” Similarly, another practitioner explained how they try to “create a tone of collaboration… [and find] shared interest that we can draw on as the overarching goal, before the conversation gets pulled back down into the weeds of the different rules and regulations.” Despite a rocky start with state regulators their first few years, they described how:

“I think that we’ve [been]… showing that we’re not just trying to get an easy way off. …We still have to get a permit, but there’s less stringent regulations around them as a system than there once was… that’s been a lot of work for us, but I think it kind of has to be. I think that the thing that has made that possible is an attitude of kind of working together as opposed to an attitude of shutting it down.”

In two states, the process practitioners used to build trust was to start small, with a temporary or experimental permit. As one state regulator explained:

“I don’t think anybody knew what regulatory bucket to put [the urine recycling project in]… And basically we wrote them a temporary permit… I think sometimes you just don’t quite know what to do, and you want to get them going, because they want to do their work… I guess we think about what would be the best approach in terms of what level does it rise to, what’s the public health risk, what’s the environmental risk?”

Another way that our team and others have found to build credibility with regulators is to cite research that demonstrates the relatively low risk of urine recycling related to common concerns around pathogens, pharmaceuticals, and per- and polyfluoroalkyl substances (PFAS)—particularly after urine is processed using practices such as pasteurization and carbon filtration [31,32,33,34,35,36]. Civil and environmental engineers, for instance, have found that viruses and antibiotic resistance genes cannot survive or are unstable in hydrolyzed urine and that storage or simple processing like pasteurization of urine can remove pathogens [32,33]; plasma reactors and activated carbon can also eliminate chemical contaminants and pharmaceuticals [34,35]. And recent tests of human urine show that regulated PFAS is at levels below detection [36]. A state regulator in another state said that such research, and the ongoing collection of data, also influenced their willingness to approve one organization’s urine recycling project, noting how: “The fact that [one organization has] done research…on pharmaceuticals and things like that after land application, that really gave them a lot of clout to partner with the university…and to publish.”

Partnerships and data from academic research, however, may not always engender trust and may be received differently depending on the particular decision-maker. Advice our team was given by one interviewee for arguing for the inclusion of urine diversion in the IPC, for instance, was that emphasizing academic research or university support might be seen as a negative. Instead, we were advised to demonstrate that the code change we were proposing is supported by treatment plant operators, plumbers, and toilet installers. Relatedly, one urine recycling advocate who presented research multiple times to a particular regulator, described how the regulator’s receptivity suddenly changed when talking to their business partner:

“We set up one of the toilets in the parking lot outside of the regulator’s office… The regulator initially said [they] just had five minutes to meet and see the toilet… my business partner is a charismatic [person] who struck up a conversation with the regulator, quickly developing great rapport. After an hour of them conversing, the regulator was willing to provide the permit…So it just further validated assumptions that regulators often…are much more open to interpretation… All to say, it’s sometimes not facts but emotions that sway regulators’ positions of “reject” or “support”.”

While physically seeing the toilet might have played a role, or the ongoing pressure that the interviewee had maintained on this particular regulator, as they reflected on why their business partner had more influence, they wondered if they personally could have had more “empathy” in earlier interactions, to understand where the regulator was coming from: “Maybe that’s where I really should have spent more time understanding… What are they about? How long have they been in their role? What are some of their own things that they really feel great about? Some areas that they have concerns regarding? …I don’t think I brought much empathy to that engagement and maybe that would have really benefited our conversation.”

3.6. Creating Precedents and Maintaining Momentum

Interviewees also indicated that creating a precedent by securing the first permit in a state may help pave the way for future permitting, but timing may also matter. In two states, the first step that practitioners requested was an experimental or temporary permit to carry out small-scale agricultural trials for research purposes (in Michigan) and to carry out small-scale wastewater collection and treatment experiments (in Vermont). The work in Michigan is still in its early stages, but in Vermont, the initial permitting process was then followed up with a 10-year permit to pasteurize and distribute UDF to area farms. This first permit in Vermont also “created the path” so that state agencies “knew exactly what to do” when a second urine recycling organization sought to permit their operation. A practitioner in another state learned, however, that subsequent permits likely need to be requested soon after the first. They described how they had secured a permit to collect and apply urine for a one-time event, but when they tried to help another group of stakeholders secure urine diversion toilet permits more than seven years later:

“No one seems to want to acknowledge that precedent has been set. And it’s often sort of dismissed like a one-off permit, and that it’s not something to follow as a model for more permanent and ongoing activities of recovering and recycling urine fertilizers… We’re constantly going back to the start as if no one has ever brought up this topic or discussed it. I think that we just need to do a better job of building and maintaining momentum so that it’s not such a slow process that it sort of just cycles back to square one.”

4. Discussion

Our findings show that the key challenge confronting efforts to establish urine recycling initiatives in the US is a lack of clarity around which sectors, or even what scales of government, “own” the decision to allow the collection and use of urine as a fertilizer. Our regulatory mapping, interviews, and action research demonstrate that urine recycling is like many complex, socio-technical innovations [114,115]: governed by multiple regulatory bodies at local, state, and national levels that cross public health, water, agriculture, and environmental regulations. While scholars argue that these types of systems-based solutions require “joined up government” [116], involving “horizontal communication” [117] and collaboration between multiple government agencies and external stakeholders, this type of policy integration is rarely achievable [118,119,120]. Outside of entirely restructuring government in this way, our findings reveal more practical strategies available to urine recycling practitioners, including ways to simplify the regulatory process to obtain approvals and reduce the risk aversion that many regulators feel when confronted with new technologies and ambiguous rulemaking.

4.1. Simplifying the Approval Process

To simplify the urine recycling approval process, one project brought all decision-makers across the system to a single meeting. This prevented the passing off of decisions to someone else and encouraged collective problem solving, resulting in regulators issuing all of the needed permits at once. In effect, these project leaders were attempting a version of “joined-up government”, but without having to permanently reorganize government institutions. When possible, this appears to be the fastest, and most logical way to deal with a circular system like urine recycling, but it also likely requires considerable political capital and skill to effectively organize and facilitate such a meeting. Alternatively, our team and other interviewees managed the permitting process as a sequential process by deciding which regulatory bodies to engage first. This approach acknowledges that government institutions tend to work in more siloed ways [116], as one interviewee put it, “in a line…[where they] hand off one thing to the next department”. For instance in Michigan, as we noted, our team learned that first getting treated urine recognized as a fertilizer by the state agriculture agency would ease future approvals needed from departments of environment and public health.

We also learned that categorizing UDF as wastewater for non-potable reuse, or as a biosolid, could require more complicated and costly permitting processes and limit the marketability of UDF. The better option seems to be customized permits like Vermont was able to secure through their solid waste beneficial use program. Although consumers and farmers have generally appeared willing to accept UDF-grown food [44,45,82], our findings further suggest that marketing UDF toward horticulture, landscaping, and non-edible crops would be a better starting point given the regulatory uncertainty around using UDF on food crops consumed raw (Figure 2) [121]. Finally, interviewees agreed that future permitting is also simplified by establishing early precedents and maintaining momentum by pursuing subsequent approvals soon after initial permits are secured. As such, we expect to see urine recycling projects to first cluster and expand most quickly in places where inspectors become familiar with urine diversion toilets, where developers can depend on prior variances as precedents, or where UDF has already been certified as a fertilizer.

4.2. Reducing Risk Aversion

The second main challenge encountered was risk aversion among regulators. As interviewees found, when faced with ambiguous rules, regulators can often choose different strategies to manage the same risk [122] when they have to rely on their professional judgement and weigh competing demands like “safety, risk, practicality, etc.” [84] (p. 12). Some regulators chose not to permit urine recycling if any risk seemed possible, leading one practitioner to feel that they would have to wait for a less receptive decision-maker to retire. Other practitioners, however, were able to build trust with regulators, reducing their concerns. In two cases, starting with temporary permits for small-scale pilots and sharing research findings built their credibility. Practitioners who worked with the regulator who talked about wearing a “gray hat” also built trust by going back-and-forth, working together to find a compromise. In another case, when a business partner was given a permit after an hour-long conversation, the person who had been denied the same permit multiple times wondered if they should have approached that regulator differently from the start to build rapport, with “empathy”. As we reflect about our work in Michigan, the interviews we carried out with regulators allowed us to approach them with empathy as well, in a sense, as we first learned about the ways that their backgrounds, responsibilities, and constraints shaped how and whether they might offer us permits for urine recycling.

4.3. Future Research

Our study addresses research gaps related to the governance of urine recycling, while also raising more questions. The sustainable transitions literature [123] calls for more comparison of the contexts that create different pathways for the widespread adoption of sustainable technologies like urine recycling. Whether it is more effective to try for sequential vs. collective regulatory approvals or whether it is possible to reduce regulators’ risk aversion will likely depend on local institutional dynamics, the strategic capacity of urine recycling advocates, and the personalities, discretion, and motivations of local regulators—all questions that deserve further study in more diverse contexts. Studies are particularly needed in Europe and the Global South where there is a higher proliferation of urine recycling projects (see Table S1 in the Supplementary Files, [10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28]), to compare the influence of unique political, social, economic, or environmental dynamics on the launch, expansion, and sunsetting of urine recycling initiatives. Cross-country comparisons could also examine the pressures believed to be motivating regulators to approve urine recycling, including water scarcity, inadequate wastewater infrastructure, climate adaptation, or demand for local fertilizer [67,124,125,126].

Future research should also examine the enabling or obstructive role that other street level bureaucrats may play in the installation and inspection of urine diverting toilets and in the distribution of UDF, such as urban planners, architects, developers, plumbers, septic haulers, and agriculture extension agents. More work is also needed to examine how the mix of crops, markets, and existing fertilizer practices shape UDF adoption and to determine more systematically if the hurdles are lower for certifying UDF for use on lawns, turf, and landscaping as opposed to food-based crops.

Finally, our study also encourages an examination of concrete examples of “anticipatory governance,” an approach to rulemaking that transition scholars argue is needed in the face of rapidly evolving environmental crises [119]. As opposed to slower, incremental “command and control” [127] oversight that creates “regulatory lags” around innovative solutions [119] (p. 242) like we saw, anticipatory governance uses an “iterative” regulation design process, “putting the state in the role of co-creator rather than gatekeeper” (p. 256). In our study, anticipatory governance appeared to be guiding the regulator with the “grey hat” who worked with practitioners to find a compromise and the example where multiple decision-makers agreed to a joint strategy session.

5. Conclusions

Widespread adoption of circular sanitation systems was unthinkable several decades ago, but intersecting issues with strained and energy-intensive wastewater systems, ongoing water pollution, costly and unreliable fertilizer supply chains, and greenhouse gas emissions [3,4,8,53,54,55,65,67,114] along with advances in urine diverting toilets and treatment technologies [30,31,32,33,34,35,36] may be creating a window of opportunity that could lead to the “global diffusion” of urine recycling in the next decade [41]. The challenge ahead for urine recycling advocates is similar to what faces environmental activists and scientists attempting to spark faster societal action around the climate crisis and other “grand challenges” [52,114,115]: to make evident to regulators that there is more risk involved in a business-as-usual scenario [128,129] and to instead see sustainable technologies like urine recycling as a form of risk mitigation [130]. With the right type of “boundary spanners” [89], like those we found strategically navigating complex regulatory environments and building regulators’ trust, this needed perspective shift could happen more quickly to help expand urine recycling to diverse contexts.