Challenges and Opportunities for Urban Water That Is Fit to Play in

Abstract

As cities in Europe and beyond recognize the flood protection, recreational, and biodiversity benefits of blue-green spaces, human interaction with urban water is increasing. This trend raises public health concerns that must be addressed by the scientific community, regulators, and the water industry. Advances in measurement and modelling have made continuous city-scale water quality monitoring for real-time risk communication a realistic goal. Achieving this goal requires quality-assured data on hydrology, water quality, drainage infrastructure, and land use, along with robust mechanistic models and a deeper understanding of human behaviour.

Risks exist, where humans and hazards meet [1]. Therefore, urban drainage systems in Europe and beyond have historically focused on separating people from waterborne hazards by quickly transporting wastewater and rainwater away from built areas. With sewage pipes, drains, urban streams and rivers buried below ground, public awareness of the urban water environment became limited. However, as cities rediscover the amenity and biodiversity value of “lost rivers”, redevelopments transform industrial docks into living spaces, ponds and swales are built for sustainable stormwater management, and Olympic swimming events are held in city centres, there is increasing human interaction with urban water. We need to understand the implications for public health and regulations [2].

In Europe, the Water Framework Directive (WFD) governs freshwater monitoring and protection but does not set microbial water quality standards. As a result, our understanding of microbial hazards in urban waters is limited. In the UK, frequent storm discharges from combined sewer systems have drawn attention to this issue, as these discharges release a mixture of runoff and raw sewage into rivers [3]. Additionally, separated surface water drainage systems designed to handle only rainwater can become polluted by wastewater via crossovers and misconnected household appliances [4]. In water-scarce regions, stormwater is increasingly being used for stream flow augmentation and groundwater recharge [5]. Potentially, this creates new pathways for the transmission of waterborne disease. Evidence shows that urban water quality is highly variable between locations and can at times be very poor [6]. To support government investment plans for improvement of aging urban drainage infrastructures [7], we need a better understanding of why urban stormwater quality fluctuates, and how it can be improved effectively.

In this context, the rapid advancement of analytical methods for water quality monitoring presents challenges and opportunities. Sensors now allow continuous monitoring of flow and some aspects of physicochemical water quality providing high-resolution geospatial data at the catchment-scale [8]. This reveals how urban water quality responds to rainfall, intermittent discharges, and other notable events [9]. Next-generation sequencing of environmental DNA (eDNA) determines numerous aspects of biological water quality in a single analysis, including microbial virulence and antimicrobial resistance traits [10]. eDNA analysis can discriminate between human and animal sources of faecal pollution [11]. Additionally, satellites and drones help with high-resolution geospatial data collection, providing insight into land use change and shifts in catchment imperviousness [12]. These technologies generate large and novel data sets that can inform machine-learning models for predicting urban hydrology and water quality [13]. However, maintaining and calibrating sensor networks, as well as managing extensive datasets, is costly. Rapid innovation in eDNA analysis hinders data comparison, as methodologies become outdated before they gain widespread use. Machine-learning models face difficulties in predicting future conditions that are not represented in the training data sets, such as changes in weather patterns that may result from climate change [14]. To elucidate trends in urban water quality, establish causes, and implement cost-effective pollution control measures, we need long timeseries of validated data and well-aligned meteorological, hydrological, physicochemical, biological, and land use records. Models with mechanistic insights are necessary for identifying urban water pollution sources and implementing effective pollution control measures. Additionally, understanding when, where, and how people are exposed to pollutants in urban water is crucial for effective risk management.

Human behaviour plays a key role in shaping public health risks from urban water [15]. Current regulations monitor microbial hazards only at official bathing sites [16], but a wider range of activities bring people in contact with urban water. Comprehensive risk assessments should consider exposure risks for those swimming, paddling, rowing, fishing, mud larking, pond dipping, or simply wading and splashing around in urban water bodies. We need to better understand how accidental water ingestion volumes vary between these activities, and when, where, and how frequently people engage in them. Beyond water ingestion, people may also get exposed to chemical and microbial hazards in urban water via dermal contact and the consumption of fish and shellfish [17]. With improved water quality monitoring and modelling, waterborne disease outbreaks can be linked to water quality at the time and place of exposures. In this way, more robust relationships can be built between exposures and ill health outcomes, addressing a major uncertainty of current risk assessment models [18]. Additionally, we need improved risk communication methods that help the public make safe decisions about water recreation [19]. Information technology and social media provide opportunities for real-time information sharing [20], but growing public scepticism about advice from the authorities poses a challenge. We need to research how to improve the public acceptance of public health messages. Citizen science and science communication through the arts provide avenues for public engagement that promotes restoration and safe enjoyment of urban water spaces. However, these initiatives need to be focused on delivering true value for the participants [21].

Given the global nature of the urban water protection challenge, measures taken by the authorities will need to consider the local status quo and public health priorities. Sharing best practice and cooperating internationally is then key to achieving the United Nations Sustainable Development Goal 6 (SDG6): safe water and sanitation for all [22].