Green Infrastructure for Sanitation in Settlements in the Global South: A Narrative Review of Socio-Technical Systems

: In the developing economies of the Global South, a fundamental challenge in the transi-tion of settlements from rural or periurban to urban is increased environmental contamination as a result of poor sanitation and sanitation management. With governments’ limited ability to connect all neighbourhoods to a city’s existing municipal water, sewerage and other services, decentralised approaches using green infrastructure offer potential to address this challenge. In addition, green infrastructure might facilitate a move towards a holistic response to manage the full water cycle. This paper presents a narrative review of green infrastructure projects, involving constructed wetlands or their variants for wastewater treatment, within vulnerable communities in the Global South. It describes the scale and scope of each project, identifies the challenges of implementation, and reflects on their outcomes for different stakeholder groups. The review demonstrates that decentralised sanitation programs using constructed wetlands for wastewater treatment can provide a range of advantages/benefits/services, dependant on the specific sociocultural, political and biogeophysical contexts of each. Issues of governance and sociocultural appropriateness, rather than technical issues, challenged the implementation of green infrastructure for sanitation in these projects. Projects must be a collaboration between the government, nongovernment organisations and the community. Whether the project is organised from top-down or bottom-up, community consultation is essential. Context will determine the role of the community in the consultation process and the type of information required to guide the design, implementation and governance of the system. In every project to provide decentralised sanitation systems, the community must be participants, not simply beneficiaries.


Introduction
A goal of the United Nations (UN) Millennium Declaration was to halve the proportion of people without sustainable access to safe drinking water and basic sanitation by 2015. Although the target for drinking water was reached, that for sanitation was not [1]. Approximately 2.5 billion people still had no access to improved sanitation facilities, and almost 900 million were still practising open defaecation [2]. In cities in developing countries, most communities are served by nonnetworked, on-site sanitation systems, i.e., septic tanks, cesspits, or private or public pit latrines (unsewered ('dry') toilets) [3,4]. In 2002, on-site sanitation systems were the predominant form of disposal of most urban dwellers in Africa and Asia and many in Latin America, leading to contamination of water resources and risks to public health. Problems arise when there is a mismatch between septic tank density and the soil's capacity to assimilate the waste stream, resulting in soil and groundwater contamination, and when the septic tanks, cesspits and pit latrines are not emptied frequently enough or the collected waste is disposed of without treatment [4]. are a low-cost technology that can provide rudimentary treatment in the management of wastewater. Different types of wetland are available, i.e., horizontal flow, vertical flow, subsurface flow and surface flow, depending on the context of the settlement. Once treated, the effluent can be used as a resource for horticultural and agricultural production, contributing to the local economy [4,9]. In such circumstances, GI as resource-oriented sanitation [15] offers the possibility of developing a circular economy [16] in which waste products are retained within the economy as resources with value.
GI also facilitates the monitoring and evaluation of the sanitation system to determine its sustainability, which is essential to achieve UN SDG6 [17,18]. Different sustainability indices have been developed for this purpose, varying in intent, focus, scale and detail. An early index [19] assesses performance of existing systems at a city scale, focusing on environmental issues and efficiency and performance of technical systems. The Water Sanitation and Hygiene (WASH) Performance Index evaluates a country's performance in water access and equity and sanitation access and equity using UN SDG indicators and data sources from the WHO/UN Joint Monitoring Program and trends in sustainability [20]. These two performance indices can guide future progress towards sustainability. In contrast, sanitation sustainability indices can use broader sets of descriptors or subindices to characterise existing or potential systems to be implemented in cities or local communities [17,18]. The Water and Sanitation Sustainability Index (WASSI) [17] is based on a five-dimensional sustainability concept related to place, permanence and persons, and uses nine descriptors and 15 indicators, including issues of governance and customer satisfaction. It is context-specific and uses local city-based data. Another sanitation sustainability index was developed to complement the WASH Performance Index by quantifying technical, social and economic aspects of a local community. Important in this index are the acceptability and public health indicators [18]. Such sanitation sustainability indices can guide decision-making in the selection, design and implementation of a sanitation system most suitable, and hence most likely to be sustainable, in a particular context.
As most studies of GI have been conducted in cities in Europe, North America, East Asia and Australia, its relevance and practical application in a wide range of contexts are not yet established [21]. There have been few studies of GI in informal settlements, with their challenges related to urban density, informality, and land tenure. This paper attempts to address this gap, with a review of projects in settlements in low and middle income countries (LMIC) in the Global South, in which GI was implemented to provide decentralised sanitation services. We were interested in the scale and scope of the GI intervention, the challenges of implementation, and the outcomes for different stakeholder groups, especially the advantages, benefits and/or services and, conversely, the disadvantages, costs and/or disservices of these programs for each group. The focus in many papers is on the technical aspects of subsurface constructed wetlands as wastewater treatment systems. This technology has great potential for treating wastewater in small and mediumsize communities because of its simplicity, reliable performance and ease of operation and maintenance [22]. The resultant effluent and byproducts can be used for irrigation, animal feed and fertiliser. In this paper, we are also interested in the social and cultural aspects associated with the implementation of these systems. As socio-technical systems, the benefits of the technology are dependent on adequate arrangements for operation and maintenance to ensure the long-term performance of the constructed wetlands, and community participation in educational programs promoting hygiene and environmental health [22]. Ultimately, we wish to establish the potential of decentralised GI for wastewater treatment in the Global South.

Methods
A systematic review was not undertaken for this paper, since these are best suited to narrowly defined questions involving quantitative data [23]. Despite its limitations, a narrative review format was adopted to best fulfil our intentions, allowing for a broader research question that would facilitate more comprehensive identification of issues within a given topic from a range of literature sources [23]. The review draws on published literature identified through a structured search process of Google Scholar, using terms related to sanitation provision, including: "green infrastructure", "nature-based systems", "constructed wetlands", "wetland", "wastewater treatment", "ecological sanitation design" and "Decentralised Wastewater Treatment Systems"(DEWATS). Searches were also conducted using the above terms in conjunction with "informal settlements". Given that we were interested in built, rather than conceptual, projects, grey literature was also considered, including reports by implementing agencies such as the WASH program and the WHO. Additional published literature was identified through the reference lists of key articles.
Publication date was not an excluding factor, and, although no geographic restrictions were included in the searches, the literature was reviewed for relevance to urban and periurban settings in LMIC. No language restrictions were placed on the search; however, only English language documents and abstracts were reviewed. As reflected in our search terms, we were most interested in the literature related to design and implementation of sanitation systems and literature relating to built projects only was included in the review. Natural GI systems that are providing wastewater treatment by convenience-rather than by design-as can occur within the unserviced informal settlement context [6,24] were not considered.
Based on the LMIC filter, our search returned projects from countries within five of the six World Bank-identified regions: East Asia and the Pacific, Latin America and the Caribbean, the Middle East and North Africa, South Asia and Sub-Saharan Africa [25]. Finally, based on data availability and the inclusion criteria defined above, 13 projects were selected. These included projects from Indonesia, Costa Rica, Nicaragua, El Salvador, Peru, Colombia, Brazil, Uganda, Pakistan, Zimbabwe, the Philippines and Nepal.
We applied a classification based on Gauss (2008), which structured project reviews under the categories: "Design and construction", "Operation and maintenance" and "Community participation in implementation" [22]. These have been identified as important topics relating to the implementation of socio-technical systems, across literature on water, sanitation and hygiene.

Results
We selected for examination 13 projects in which constructed wetlands were used as GI to manage sanitation in settlements in the Global South. Descriptions of these projects differed, depending on the aim of the sanitation project and the aim of the authors in writing about it. Thus, in examining each project, direct comparisons may not be possible. Nevertheless, the critical aspects of the projects of interest in this study were the scale and scope of the intervention, and the challenges of implementation.
The scale and scope, with details of location, for each project are given in Table 1. This information was not always explicit in the description of the project and in some cases had to be inferred, indicated by a question mark. On this basis, seven projects were in periurban locations, two were rural, and four were urban. Location was not indicative of scale of operation, though. The urban constructed wetlands in Pereira, Colombia, catered for 280 people, whereas constructed wetlands in rural locations might cater for as few as four households in Santa Elena-Monteverde, Costa Rica, or as many as 5000 people in Nemanwa, Zimbabwe. Wetlands constructed in terrestrial periurban locations generally served upwards of 1000 people. In contrast, floating sanitation gardens in waterside villages in Indonesia were designed to serve two households. The preponderance of constructed wetlands in periurban locations could reflect the availability of space on the edge of cities rather than within them, for the provision of GI. • Flush toilets and greywater connected to storage tank and 2 SS constructed wetlands. • Outflow used by 2 local farmers who gave land rights for system construction.  As we are interested in the implementation of GI in these projects as a socio-technical system, we focused on those aspects of the system where the technology could interact with the community and might be influenced by its social and cultural aspects. Hence, each project was analysed to reveal information about:

1.
Operation and maintenance (O&M) Who does it and how is it financed? How are the roles and responsibilities divided and what falls to communities?

Technical construction
Availability of local experience and materials-new technologies/approaches. Opportunity for capacity building.
The results are presented in Table 2.
The results are constrained by the information available in each project description. Nevertheless, for most we have been able to extract the relevant detail or infer it from the published material. The analysis of the results reveals that there were six approaches to the provision of GI for sanitation services in the 13 projects ( Table 3). The BIOSANTER project in Indonesia is excluded from Table 3 as the data were insufficient to allocate it to a group. It was government-initiated but the extent of community involvement in consultation before the project was implemented and in management of the floating sanitation garden is unclear. In seven projects, the importance of community participation to implementation of the project was emphasised. These are highlighted in bold in Table 3. The purpose of community participation, though, differed between these seven projects, dependant on the sociocultural or biogeophysical context and needs of each. In Pakistan, Uganda and the Philippines, community participation informed the context-specific design and location of the toilets and associated infrastructure. In Alagohinas, Brazil, and Pasto, Colombia, it identified community sanitation and health priorities. In El Salvador and Nepal, it enabled the local community to operate and maintain the sanitation wastewater system, including the constructed wetlands.    Design of context-specific infrastructure: Community participation in the Pakistan project was critical to an understanding of the sociocultural context of the project. In this case, sociocultural context included the community's perceptions of toilets and its cultural and religious practices and prohibitions related to defaecation, cleansing and cleanliness. This understanding was essential to ensure that the sanitation service for Machaki Village was designed to reflect its residents' values and practices and so would be used by them. Consequently, water-flushed toilets were adopted, rather than the usual dry toilets, and an underground sewerage system leading to constructed wetlands for treatment of wastewater, with water and nutrient reuse. This top-down system, in which the government provides water services, is the convention in Pakistan and an expectation. Nevertheless, in this project, the community did make an in-kind contribution to 20% of the cost. Similarly, community consultation in Kisoro, Uganda, also informed the design of the infrastructure, focused more on hydrogeological and other physical characteristics of the village rather than its residents' cultural and religious beliefs and values. The location of the village atop its only water source, soil structure and land scarcity determined the use of four sets of different components, some involving water-borne sanitation and others dry sanitation. Nevertheless, "social/emotional aspects" were considered as important, if not more so, as "rational processes" in decision-making [30] (p. 7). Effective community consultation was essential to reveal subjective responses to inform decision-making. So, too, in GK Fishermen's Village, Bayawan City, Philippines, the NGO behind the project, Deutsche Gesellschaft für Technische Zusammenarbeit, engaged in extensive community consultation to ensure that the infrastructure was best suited to the local sociocultural context. Community consultation was cyclic, involving the training of local participants, readapting, implementing, and retraining.
Identification of community sanitation and health priorities: In 2001, the Alagohinas municipality in Brazil developed a municipal environmental sanitation policy. A participatory process between local government, the local community and the local university then followed, to develop a municipal sanitation plan for Alagoinhas. Inevitably, community priorities for health and environmental protection would have been revealed. As a result, various sanitation projects, including constructed wetlands to treat wastewater in Alagoinhas, were implemented. Community participation in Pasto, Colombia, also revealed community priorities for health and environmental protection. This participation included consultation with community leaders, hygiene promotion and environment education. One of the priorities identified was for the community to take ownership of the sanitation project and to manage it, although the local water and sanitation utility is currently managing the system [22].
Management of sanitation wastewater system: In El Salvador and Nepal, community participation was geared towards enabling the local community to assume O&M responsibilities for the project under a management committee. In both projects, the local community recognised the importance of sanitation and initiated the project, with support from NGOs. In El Salvador, the local community in San Jose Las Flores worked with the Swiss Agency for Development and Cooperation and the local NGO Pro-Vida to implement a project based on a pilot plant successfully constructed in Masaya, Nicaragua. It elected a Municipal Water and Environmental Sanitation Committee, which promoted the project. The project involved more than a sewerage system and constructed wetlands. It included on-site sanitation for residents outside the most densely populated part of the village, community development and intensive hygiene education. The committee manages the constructed wetland system, and appointed a plant operator from the community. This person was trained at the pilot plant in Masaya, and has trained members of the local committee and a member of a local youth group to ensure continuity of operation of the system in his absence. Users of the system pay a small fee. In Nepal, the NGO Environment and Public Health Organisation (ENPHO) had introduced decentralised wastewater technology to the country in 1997. The local Sunga community in Madhyapur Thimi municipality initiated the project to manage their wastewater. With WaterAid, ENPHO worked with a management committee selected by the community, comprising 17 members representing local leaders, community-based organisations, the community, the municipality and local schools. This committee chose the site for the constructed wetland and lobbied the municipality to acquire it. The community contributed labour for construction, with technical support from ENPHO. Then the management committee assumed responsibility for the system's operation and maintenance, with a caretaker, with funding derived from an annual contribution by the municipality and from nominal connection fees from users.
The distribution of the advantages, benefits and/or services and disadvantages, costs and/or disservices in each project are shown in Table 4. In general, in these projects, residents acquired advantages, benefits and services, with few disadvantages, costs and disservices, either collectively or individually. In each case, the residents obtained sanitation services supported by a constructed wetland, reedbed or floating sanitation garden. It can be assumed that their sanitation hygiene improved and so too their health. Certainly this would be expected in those projects in which hygiene practices were promoted through community engagement activities, e.g., El Salvador. The treated wastewater was used for irrigation in horticulture or agriculture, and solid byproducts used as fertiliser or fuel. In the Philippines, biogas was generated. The amenities of the local area were enhanced by the development of constructed wetlands, restoration of local landscapes, and the provision of green space. In Lima, Peru, wind erosion was mitigated. The environmental health of nearby waterways was improved, with better water quality and increased flow. Harvested biomass from the constructed wetlands or reedbeds was used as fodder. In several projects, individual residents, as a member of the management committee, plant operator or caretaker, developed management skills. Only in four projects did residents incur any financial cost for the operation and maintenance of the sanitation system. In most of these, a community committee of management assumed responsibility for the system and charged its users (the residents) a tariff or connection fee. In general, government or municipal funding met all costs.

Discussion and Concluding Remarks
Decentralised sanitation as GI has been implemented effectively in the 13 projects in LMIC in the Global South examined in this review. Generalisations about the best way to provide sanitation are neither possible nor desirable as context is critical in each project. An important finding has been the contextual specificity of each project and the need for a context-specific sanitation solution for each. A form of GI-a vegetated treatment systemwas included in the mix of components to deliver a sanitation service, e.g., constructed wetland, floating sanitation garden or reedbed. Its exact design was determined by the political, sociocultural and biogeophysical contexts of the settlement and the availability of suitable materials and financial resources. In these socio-technical systems, the social aspect of each is as important as the technical aspect to ensure an effective system.
The uneven detail provided in each project limits their comparative analysis. However, the detail of two projects [9,37,38] and inferences from the others reveal the importance of coproduction in the design and development of the sanitation systems, their construction, O&M, and dissemination of complementary skills and knowledge, e.g., hygiene practices, to maximise the benefits of the systems. In some projects, delivery of the sanitation service was driven from the top-down, initiated, funded and implemented by the government, or by the government with support from an NGO. In other projects, it was initiated from the bottom-up, by the local community working with a level of government or an NGO. In yet another, it was initiated and implemented by a local community working with an NGO, with government funding for the construction of the system, which was then managed by the community. In each project, the specific political, biogeophysical, social and cultural contexts determined the mix of actors in the coproduction process. In all projects, however, the community was involved as active participants, not just as beneficiaries [39].
Writing about nature-based solutions for infrastructure in the Pacific, Zari (2019) emphasised that implementation demanded partnerships that embraced "community ownership, communal responsibility and creating consensus through dialogue" [39] (p. 8). Multistakeholder partnerships between governments, NGOs, and communities needed to align with customary practices. Such practices are components of a community's sociocultural context. Thus, sociocultural context is as important as biogeophysical context in establishing how the community will contribute to coproduction. This was evident in the Pakistani project [9]. The community expectation was that the government would supply sanitation and water services at minimal or no cost. Coproduction took the form of extensive input on social and religious beliefs, values, and practices involving water and defaecation, sewage and cleanliness. The community gained ownership through the design of a sanitation system specific to their precise needs. In addition, they contributed 20% of the cost through the supply of raw materials and labour in the construction of the treatment wetland. Consensus on the best system for the community was created by extensive consultation with the community, who sought guidance from their religious leaders. Finally, communal responsibility was established by a design that reflected the religious and sociocultural practices of the community. In contrast, coproduction in the Nepalese project [37,38] was more comprehensive, with the community participating in every stage of the project. The community owned the project from the outset, initiating it with support from an NGO and local government. It is responsible for its operation and maintenance, again with support from local government. No doubt, the consensus required to achieve this was reached through extensive dialogue.
Both the Pakistan and Nepal projects demonstrate the value of communities working with government and nongovernment agencies to achieve sanitation services. Bottom-up approaches to GI without state involvement are often limited in available resources and short-lived because of the precarious living conditions of many residents in settlements in LMIC [40]. Residents have the motivation and social capacity to identify, prioritise, plan and implement projects to meet community needs, with or without government or NGO assistance, as demonstrated by the Nepal project, but they need government, NGOs or professionals to provide an enabling environment for the community-based approach to succeed [41,42]. On their own, self-help initiatives are coping strategies only [41]. Topdown approaches are constrained by a lack of adequate material and human resources, and various ecological, institutional, political and cultural challenges [1,43]. Governments might have insufficient resources, including financial resources, to implement a long-term strategy, necessary for development of infrastructure, or they might be ineffective in their social and regulatory roles [44]. Government policy might specifically limit the provision of sanitation infrastructure to interim solutions, such as periodic waste collection and chemical toilets (usually Ventilated Improved Pits) [42]. Such limitations might result from tensions between a responsibility to service what might be regarded as informal settlements, a need to discourage their growth, and a belief that they are temporary housing solutions until residents are relocated into housing projects or the settlements are upgraded to become "formalised" [8]. Lack of space or distance from bulk water infrastructure or wastewater treatment plants might prevent centralised, sewerage systems. Local soil and hydrological regimes, e.g., high watertable, might lead to ground or surface water pollution by dense onsite greywater dispersal systems [1,4,8]. Thus, hybrid approaches involving government, NGOs and communities working together are most likely to produce sustainable sanitation solutions, which are likely to rely on decentralised systems.
Challenges still remain, however, once the system is chosen and designed. Technical challenges exist in the construction of the system, often in isolated locations with possibly difficult access to the building materials and construction skills common in the Global North. In the projects explored here, many of the local communities, working with the government or an NGO, were innovative and focused on problem solving. Western building materials were often replaced with locally available materials. For example, in the BIOSANTER floating sanitation gardens in Indonesia, local materials were used in the construction of the toilet, biofilter and floating sanitation garden, including waste in the filter medium [26]. In Nepal, the design of the constructed wetland itself was altered to fit with local conditions [37,38]. In many projects, local aquatic plants were used in the constructed wetlands, reedbeds or floating sanitation gardens [35,36] and in Costa Rica and Peru, where there were no natural wetlands, suitable local aquatic plants were chosen [22,27,28]. These aquatic plants were also productive crop plants in some projects, thereby contributing to the local community's economic base (e.g., [28,[32][33][34]). Once the technical system was built, governance issues had to be resolved. For example, O&M had to be arranged to ensure that the system functioned as intended and delivered the service satisfactorily. Funding for O&M had to be obtained, and also the technical and managerial skills to undertake it. Tied up with O&M are ethical issues and notions of equity [8]. Pan et al. (2015) explain that equity is "an 'ethical concept' related to notions of 'social justice, fairness and human rights', based on need as a foundation for the allocation of resources" [8] (p. 222). They add that this concept is value-laden and political, as is sustainability, and warn of a tension between meeting short-term goals and a long-term vision for sustainable and equitable sanitation services. Nevertheless, we regarded the projects here as ethical if O&M was undertaken in a way that reflected the values and beliefs of the community and the community was consulted about management expectations [43]. Eales et al. (2013) advocate for a comanagement approach, distinguishing between above-ground and below-ground activities [45]. The former, which have direct benefits to communities, are day-to-day activities such as easily detectable minor repairs and are more appropriate for community-based management. The latter, which do not benefit communities directly, are more complex maintenance works-such as desludging-and are undertaken by local government or outsourced to private partners [45]. Sociocultural context is critical here. What is regarded as ethical in Pakistan might not be ethical in Nepal. Sociocultural context and the consequent community consultation also determined the appropriate contextual adaptation of the sanitation system in each project. It was not always effective, e.g., the chicken project in Mupandawana, Zimbabwe [28,[32][33][34]. Duckweed was to be harvested from the wastewater treatment pond for reuse as chicken feed for broilers. The failure of the project was attributed to negative sociocultural attitudes to wastewater reuse. Appropriate community participation should have revealed such negative attitudes. Collaboration with the community must be productive to ensure "an inclusive and sustainable urban future" [40] (p. 79).
These challenges, and the ways in which they were addressed in each project, reinforce the importance of community participation in devising the sanitation project from the outset. Some of these projects are examples of "organised eclecticism" [43] (p. 15), in which there is a mix of technologies and strategies, at different scales, with different financial and governance arrangements, designed as fit-for-purpose, using both technical and socio-scientific knowledge, for the specific political, sociocultural and biogeophysical circumstances of a settlement. Oosterveer and Spaargaren (2010) describe this as a Modern Mixtures approach, which must be ecologically and institutionally sustainable, accessible, particularly for the poor, institutionally and technically feasible, resilient and robust [43]. It is not an inferior substitute, to be replaced in the future by a large-scale, highly technical centralised system but a modular approach that combines the most appropriate mix of technologies and governance options, best suited to the context. As this review has shown, selection of this mix relies on technical and sociocultural factors. Oosterveer and Spaargaren (2010) suggest that this selection should be augmented by environmental flow analysis [43].
The selection of the mix should also be informed by an understanding of the local economy and the contribution that byproducts of a sanitation system can make to establishment of a circular economy. Resource-oriented sanitation systems have the potential to generate an income for the community [15,16,46]. When the costs of an entire sanitation system, from pre-toilet to post-toilet, are calculated, including the use of treated urine and faeces as fertilizer or soil conditioner and the income from sale of agricultural, horticultural or other products derived from the system, resource-oriented sanitation systems are economically beneficial [11]. Critical to the success of this is the willingness of the local community to reuse the waste byproducts [15,46]. Traditional sociocultural practices in some countries, e.g., Korea, Japan and Vietnam, might support the use of harvested human waste for agricultural production [46]. In others, e.g., India, traditional uses of animal urine and manure provide a precedent for use of human waste, which was acceptable to about 50% of farmers in a study in Vellore. However, they preferred that their neighbours used the human waste as fertilizer and soil conditioner rather than their friends, family or colleagues [15]. Several projects in this review used treated wastewater to irrigate crops, with apparent success. The one failure involved the project in Mupandawana, Zimbabwe, in which duckweed harvested from the wastewater treatment pond was to be used as chicken feed. The potential of the sanitation system to create a resource, which could have contributed to the local economy, was lost, as was the opportunity to ensure the sustainability of the sanitation system [11]. This again highlights the importance of extensive and early consultation with all sanitation system stakeholders, including producers and consumers, in the system's conceptualization, design and implementation [15].
The advantages, benefits and services, and conversely the disadvantages, costs and disservices, were treated collectively in this paper, mostly because of the limited detail provided in the descriptions of each project. However, various ecosystem services have been related to GI [47] and can be expected to occur as a consequence of its implementation in the projects of this study. Before the various projects were initiated, the communities would already be deriving benefits from many ecosystem services in nearby natural and seminatural areas, including local landforms, vegetation, gardens, waterscapes and agricultural areas, by virtue of their location in "ecologically significant, environmentally sensitive and/or biodiversity-rich places within cities" [6](p. 24) or through their agricultural activity. Implementation of the sanitation projects using GI would inevitably deliver more ecosystem services [6]. Diep et al. (2019) warn that problems can arise if a primary objective of the GI is to protect ecologically fragile areas, when removal of residents might be necessary [21]. However, this was not reported in any of the projects in this review.
In several projects, the supplementation of water supply by effluent was an advantage/benefit/service from implementation of the decentralised wastewater treatment.
Treated wastewater was used for environmental flows, crop irrigation and other purposes. To maximise the benefits of GI and increase the efficacy of WASH programs, CRC for Water Sensitive Cities (2017) argues that a holistic, integrated approach is essential. Acknowledging that delivering effective WASH programs is "necessarily different and more complex" [4] (p. 26) than in the Global North, they suggest that a combination of interventions that take into account context-specific social and biophysical factors at a range of scales should underpin funding policies. This aligns with the Modern Mixtures approach of Oosterveer and Spaargaren (2010), in which the entire water cycle can be managed [43]. Sinharoy et al. (2019) suggest that this might not be appropriate in all situations [1]. The provision of sanitation has lagged behind provision of water services worldwide, especially in urban areas. They suggest that it might be useful to consider them separately, "to tease out the separate challenges that have hampered the expansion of sanitation in dense urban environments" [1] (p. 6). The conclusion, of course, demonstrated by this narrative review, is that every community differs and the appropriate WASH service and its cobenefits must be unique, determined by political, biogeophysical and sociocultural contexts. A holistic approach might be the solution in one location but not another. Nevertheless, GI has great potential to contribute to WASH programs in the Global South. However, careful planning and comprehensive community participation with government and nongovernment entities are essential to determine the right socio-technical system for the right place.
More information is required to fully understand the success of the projects examined in this review, in particular relating to acceptance of the byproducts from the wastewater treatment for use, the methods of community consultation, and the hygiene education programs implemented for community members. In addition, it would be interesting to determine the sustainability of each system by applying a sustainable sanitation index, and to determine the contribution of the systems to establishing a circular economy for each community. These offer potential for further studies.  Institutional Review Board Statement: Ethical review and approval were waived for this study because data were accessed from published sources. There was no direct involvement of human participants in this study.