Circular systems can drive big reductions in cities’ freshwater use

Around 40% of the EU population is affected by water scarcity, presenting an urgent need for efficient ways of managing freshwater supplies. Addressing the risk of depletion of municipal water supplies is particularly important in heavily populated urban areas. The Water Framework Directive is the foundation for water policy in Europe, and the 2025 Water Resilience Strategy aims to promote water security and a circular approach to water management. 

A new study offers useful insights, looking at how utility companies can reduce freshwater withdrawals and also make long-term cost savings. The researchers note that many cities have a large footprint on local and regional water resources, with most water utility companies using ‘flow-through’ or ‘open-loop’ systems where they withdraw water from raw water sources (e.g. rivers, groundwater aquifers), deliver it to customers, collect and treat waste water, and discharge the treated wastewater to local water sources – without recycling this for potable (drinkable) or non-potable uses. 

They therefore constructed a simulation model based on a hypothetical city in a high-income country and compared a baseline open-loop urban water system to circular water systems incorporating a variety of efficiencies such as reducing leakages, implementing education interventions to reduce residential water use, and introducing the use of treated wastewater as potable water. They also considered the effects of adding a desalination plant.

The model calculated flows through network ‘nodes’, where water is treated or used, and links connecting these, showing where leakages might occur, water losses, and related capital costs. It assumed a baseline demand of 200 litres of water per capita per day (residential users), 100 000m³ for non-residential users, and leakage of 30% between the raw water intake facility and customers. Policy interventions then applied to the model included reducing leakage to 10%, reducing residential water use, reuse of 30%-60% of treated wastewater, and incorporating a desalinisation facility.

The researchers found that a combination of three policy interventions could reduce freshwater withdrawals by up to 60% compared to the baseline – specifically, reducing leakage from 30% to 10%; making further effort to reduce demand from 200 to 130 litres per capita per day (denoted LPCD); and reusing 60% of treated, potable water on longer timescales. The system-wide costs would be lower than for the baseline, despite the cost of necessary infrastructure, repairs and upgrades. 

The impact of recycling treated wastewater was substantially greater than focusing only on reducing demand and leakage, the findings show. Recycling wastewater for potable use transforms the system from an open-loop to a closed-loop system: some water that enters the system does not exit the system.

Adding a desalination plant (withdrawing 200 000 m³ of saltwater per day and producing 100 000 m³ of potable water) to this policy mix could reduce raw water extraction by a further 14%, for a total reduction of 74%. This increases costs by 3% compared to the open loop system but may not be needed in many locations, say the researchers. 

However, it should be noted that desalination facilities bring their own environmental impacts: they consume large amounts of energy, emit greenhouse gases and other air pollutants, and discharge toxic brine as a byproduct, which can degrade and contaminate marine ecosystems if released to the sea. As such, innovation in desalination is needed.

The researchers also acknowledged that the costs of losses at each node are difficult to estimate and location-specific, as utility companies often do not have such data. Additionally, they note that the costs of system upgrades will likely need to be passed on to households and non-residential users, which may be unpopular and require public education campaigns to explain the continuing need for lower usage despite higher bills. Nevertheless, the model highlights the value of reducing residential water use, and particularly the value of employing facilities to enable re-use of treated wastewater.

Reference: 

Whittington, D. and Chandrasekaran, M., 2025. The economics of a circular urban water system. Environmental Research Letters. https://iopscience.iop.org/article/10.1088/1748-9326/ade904/meta

To cite this article/service:

“Science for Environment Policy”: European Commission DG Environment News Alert Service, edited by the Science Communication Unit, The University of the West of England, Bristol.

Notes on content:

The contents and views included in Science for Environment Policy are based on independent, peer reviewed research and do not necessarily reflect the position of the European Commission. Please note that this article is a summary of only one study. Other studies may come to other conclusions.