Case study: Water reuse & recycled water systems — a city or utility pilot and the results so far

Water scarcity is no longer a distant projection confined to arid regions. European cities that once considered their freshwater supplies inexhaustible are now facing persistent drought cycles, declining aquifer levels, and regulatory pressure to reduce abstraction from rivers and groundwater. In response, several utilities across the continent have invested in advanced water reuse systems that treat wastewater to standards suitable for irrigation, industrial cooling, aquifer recharge, and in some cases indirect potable supply. This case study examines three pilot programs in detail, focusing on the design choices, capital costs, measured performance, and governance lessons that other jurisdictions can apply.

Why It Matters

The European Environment Agency reported in 2025 that 30% of the EU population lives in areas experiencing water stress during at least one month per year, up from 18% a decade earlier. Southern European countries including Spain, Italy, and Greece face chronic deficits, but even traditionally water-rich nations such as Germany, the Netherlands, and the United Kingdom have experienced unprecedented low-flow events in recent summers. The 2024 revision of the EU Urban Wastewater Treatment Directive explicitly encourages member states to promote water reuse where environmentally appropriate, and the EU Water Reuse Regulation (2020/741), which took effect in June 2023, established minimum quality requirements for agricultural irrigation using reclaimed water.

From an economic standpoint, water reuse offers municipalities a locally controlled supply that is largely immune to the hydrological variability increasingly caused by climate change. Unlike desalination, which requires access to coastal sites and substantial energy inputs (typically 3 to 5 kWh per cubic meter), advanced wastewater recycling typically consumes 0.5 to 1.5 kWh per cubic meter depending on the treatment train and target quality. The cost differential matters significantly for inland cities and regions where desalination is not feasible.

The environmental case is equally compelling. Conventional wastewater discharge into rivers and coastal waters, even after tertiary treatment, introduces residual nitrogen, phosphorus, and micropollutants into sensitive ecosystems. Closed-loop reuse systems capture these nutrients for beneficial use while reducing the volume of treated effluent released into waterways. In regions subject to the EU Water Framework Directive's environmental quality standards, water reuse provides a pathway to meet both ecological flow requirements and growing urban demand.

Pilot Design and Context

Pilot 1: Sabadell, Catalonia, Spain

Sabadell, a city of approximately 215,000 in metropolitan Barcelona, launched its advanced water reclamation project in 2021 through a partnership between the municipal water utility Companyia d'Aigues de Sabadell (CASSA) and the Catalan Water Agency (ACA). The Catalonia region had experienced four significant drought episodes between 2005 and 2023, with the 2022 to 2024 drought being the most severe on record. Reservoir levels across the Ter and Llobregat basins dropped below 25% capacity, triggering emergency water restrictions affecting 6 million residents.

The Sabadell pilot treats secondary effluent from the Riu Sec wastewater treatment plant through a multi-barrier process consisting of ultrafiltration membranes, reverse osmosis, and UV/advanced oxidation. The treatment train produces water meeting Class A standards under the EU Water Reuse Regulation, suitable for all agricultural irrigation types including drip irrigation of food crops consumed raw. Design capacity is 10,000 cubic meters per day, with an initial operational target of 6,000 cubic meters per day supplying agricultural irrigation in the Valles Occidental comarca and urban landscape irrigation within the city.

Capital investment totaled EUR 18.2 million, funded through a combination of ACA grants (45%), EU Cohesion Fund support (30%), and CASSA's own capital program (25%). Operating costs in the first two years averaged EUR 0.38 per cubic meter, compared to EUR 0.52 per cubic meter for imported water from the Ter basin and EUR 1.10 per cubic meter for desalinated water from the Barcelona metropolitan desalination plant.

Pilot 2: Braunschweig, Lower Saxony, Germany

Braunschweig operates one of Europe's oldest and largest agricultural reuse systems, but a 2022 modernization program introduced advanced treatment and digital monitoring that transformed the operation. The Steinhof wastewater treatment plant has supplied treated effluent for irrigation of 3,000 hectares of farmland since the 1950s, but the upgrade, completed in 2024, added membrane bioreactor technology, ozonation, and granular activated carbon filtration to address micropollutant removal. The modernization was driven by Germany's updated Oberflachengewasserverordnung (Surface Water Ordinance) and growing concerns over pharmaceutical residues in irrigation water.

SE|BS (Stadtentwasserung Braunschweig GmbH), the municipal wastewater operator, invested EUR 42 million in the upgrade, with EUR 12 million provided by the German Federal Ministry for the Environment's Water Innovation Fund. The system now produces 30,000 cubic meters per day of reclaimed water meeting quality parameters comparable to EU Class A, supplying both agricultural irrigation and industrial cooling water to the Volkswagen plant in nearby Wolfsburg.

Pilot 3: London Tideway, United Kingdom

Thames Water's Beckton Water Recycling Plant, commissioned in late 2024, represents the United Kingdom's first large-scale indirect potable reuse facility. Located adjacent to the Beckton Sewage Treatment Works in East London, the plant treats secondary effluent through ultrafiltration, reverse osmosis, and UV advanced oxidation before injecting the purified water into the Lee Valley chalk aquifer for subsequent abstraction by drinking water treatment plants. Design capacity is 150 megalitres per day (150,000 cubic meters per day), with initial operation at 50 megalitres per day.

The facility was driven by Thames Water's 2024 Water Resources Management Plan, which projected a supply-demand deficit of 350 megalitres per day by 2040 for the London region. Capital cost for Phase 1 was GBP 750 million, funded through Thames Water's regulated asset base with costs recovered through customer bills over a 60-year asset life. The Drinking Water Inspectorate and Environment Agency jointly established a bespoke regulatory framework for the scheme, drawing on decades of experience from Australia, Singapore, and Namibia.

Measured Outcomes

Water Supply Reliability

The Sabadell system delivered 1.82 million cubic meters of reclaimed water in its first full year of operation (2023), displacing an equivalent volume of surface water abstraction from the heavily stressed Llobregat basin. During the peak of the 2023 drought, when conventional irrigation supplies were reduced by 60% under emergency restrictions, the reclaimed water system maintained full supply to connected agricultural users, preventing an estimated EUR 4.2 million in crop losses.

Braunschweig's upgraded system achieved 99.2% operational availability in 2024, delivering 9.1 million cubic meters of reclaimed water. The transition from basic treated effluent to advanced reclaimed water enabled a 35% expansion in the irrigated area from 3,000 to 4,050 hectares, while pharmaceutical micropollutant concentrations in the reclaimed water decreased by 97% compared to pre-upgrade levels.

Thames Water's Beckton facility produced 12.3 million cubic meters during its first nine months of operation, with treated water quality consistently exceeding World Health Organization drinking water guideline values for all monitored parameters. Aquifer injection monitoring confirmed no adverse impacts on groundwater quality, with independent verification by the British Geological Survey.

Energy and Carbon Performance

Energy consumption across the three pilots varied according to treatment intensity. Sabadell's system consumed 0.82 kWh per cubic meter, comparable to the lower end of the global range for advanced reuse systems. Braunschweig's system, which includes ozonation for micropollutant destruction, consumed 1.15 kWh per cubic meter. The Beckton facility, producing indirect potable quality water through a full advanced treatment train, consumed 1.45 kWh per cubic meter.

When compared against the alternatives each system displaced, however, the carbon accounting favored reuse in every case. Sabadell's reclaimed water embodied 0.28 kg CO2e per cubic meter, compared to 0.45 kg CO2e for imported surface water (including pumping over mountain passes) and 1.85 kg CO2e for desalinated water. Braunschweig's system produced reclaimed water at 0.41 kg CO2e per cubic meter, compared to the 0.55 kg CO2e per cubic meter that would have been required for expanded groundwater abstraction and treatment. Thames Water estimated the Beckton facility's carbon intensity at 0.52 kg CO2e per cubic meter, roughly half the 1.05 kg CO2e per cubic meter projected for a reservoir-based alternative.

Water Quality Compliance

All three pilots achieved compliance with their respective regulatory quality standards in over 99.5% of routine samples during the reporting period. Key parameters monitored included:

Parameter	Sabadell (EU Class A)	Braunschweig (Custom Standard)	Beckton (DWI Potable)
E. coli (CFU/100mL)	< 10	< 10	< 1
Turbidity (NTU)	< 1.0	< 0.5	< 0.1
Total nitrogen (mg/L)	< 10	< 5	< 1
Pharmaceutical removal	> 90%	> 97%	> 99.9%
PFAS removal	Not monitored	> 85%	> 99%

Governance and Public Acceptance

Public communication proved essential in all three cases. Sabadell invested EUR 350,000 in a public engagement program that included farmer training workshops, school visits to the treatment facility, and a real-time water quality dashboard accessible online. Surveys conducted 12 months after launch showed 78% of residents supported the reuse scheme, up from 52% before the engagement campaign.

Braunschweig benefited from its long history of agricultural reuse, which normalized the concept over decades. However, the micropollutant upgrade was partly driven by public concern over pharmaceutical residues detected in studies of vegetables grown with reclaimed water. The utility framed the investment as a response to community health concerns, which increased public confidence and political support.

Thames Water's indirect potable reuse scheme faced the steepest public acceptance challenge. The utility commissioned a three-year public engagement program beginning in 2021, including deliberative workshops, taste tests, and visits to operational reuse facilities in Australia and Singapore. By project launch, independent polling showed 67% public support in the London region, compared to only 38% at the start of engagement. Crucially, the "environmental buffer" of aquifer injection provided a psychological and practical separation between treated wastewater and drinking water that pure direct potable reuse would not have offered.

Regulatory frameworks differed significantly across the three jurisdictions. Spain operated under the harmonized EU Water Reuse Regulation, providing clear quality standards and risk management requirements. Germany lacked a federal water reuse regulation at the time of the Braunschweig upgrade, requiring the utility to negotiate custom quality standards with the Lower Saxony Environment Ministry. The United Kingdom developed a bespoke regulatory pathway through collaboration between the Drinking Water Inspectorate, the Environment Agency, and Defra, creating a precedent that other UK water companies are now seeking to follow.

Transferable Lessons

Multi-barrier treatment design is non-negotiable for public and regulatory confidence. All three pilots employed treatment trains with multiple independent barriers to pathogen removal. This redundancy provided the safety margin that regulators and the public required, even though individual treatment stages could theoretically achieve target quality alone.

Economic viability depends on the cost of the alternative, not on the absolute cost of reuse. In all three cases, reclaimed water was cheaper than the next best alternative supply source. However, absolute costs varied from EUR 0.38 to GBP 0.85 per cubic meter depending on treatment intensity and local factors. Jurisdictions evaluating reuse should benchmark against their specific alternative supply costs, not against generic comparisons.

Public engagement must begin years before construction, not at commissioning. Thames Water's three-year engagement program and Sabadell's extensive outreach both demonstrated that early, transparent communication is essential. Utilities that announce reuse schemes without prior community engagement face much higher opposition rates.

Real-time monitoring and public data access build trust over time. Sabadell's online water quality dashboard and Braunschweig's monthly public reports transformed abstract safety claims into verifiable data. This transparency proved more effective at building public confidence than any amount of marketing.

Regulatory clarity accelerates deployment. Spain's implementation proceeded most quickly, benefiting from the EU Water Reuse Regulation's harmonized standards. Germany and the UK faced delays of 12 to 18 months while custom regulatory frameworks were developed. Jurisdictions without established reuse regulations should prioritize policy development alongside technical planning.

Action Checklist

• Assess current and projected supply-demand gaps using climate-adjusted hydrological models
• Benchmark the cost of reclaimed water against all feasible alternative supply sources including desalination, reservoir expansion, and demand reduction
• Design multi-barrier treatment trains appropriate to intended end uses, with independent redundancy for critical pathogen removal
• Engage public health regulators early to establish quality standards and monitoring requirements before final design
• Launch public engagement programs at least 24 months before construction, including site visits, deliberative workshops, and transparent data sharing
• Install real-time monitoring with public-facing data dashboards to build ongoing community confidence
• Negotiate funding structures that leverage EU, national, and regional grants alongside utility capital programs
• Establish performance benchmarks for energy consumption, water quality compliance, and operational availability from the first year of operation

FAQ

Q: What is the typical cost range for advanced water reuse systems in Europe? A: Capital costs range from EUR 150 to EUR 500 per cubic meter per day of installed capacity, depending on treatment intensity and local construction costs. Operating costs typically fall between EUR 0.30 and EUR 0.90 per cubic meter. Systems producing agricultural irrigation quality water (EU Class A) are at the lower end, while indirect potable reuse systems are at the higher end. All costs should be compared against the specific alternative supply source being displaced.

Q: How do European water reuse regulations compare to those in the United States or Australia? A: The EU Water Reuse Regulation (2020/741) provides harmonized minimum quality requirements for agricultural irrigation, with member states permitted to set stricter standards. It does not currently address potable reuse. The United States lacks federal reuse regulation, with standards set by individual states; California's Title 22 is the most comprehensive. Australia's Australian Guidelines for Water Recycling cover all end uses including indirect and direct potable reuse, making them the most comprehensive global framework. European regulators are increasingly looking to Australia's guidelines as a model for expanding reuse beyond agricultural applications.

Q: What are the main barriers to scaling water reuse across European cities? A: The primary barriers include fragmented regulatory frameworks (especially in countries without established reuse regulations), public acceptance concerns driven by the "yuck factor" associated with recycled wastewater, the capital cost of retrofitting treatment plants with advanced treatment stages, and the energy requirements of membrane-based processes. Of these, regulatory clarity and public acceptance are typically more constraining than technical or economic factors.

Q: How do water reuse systems perform during drought conditions? A: Water reuse systems provide drought-resilient supply because their feedstock (municipal wastewater) remains largely constant regardless of rainfall. During the 2022 to 2024 Catalonia drought, conventional water supplies were cut by 40 to 60%, while Sabadell's reuse system maintained full output. This counter-cyclical reliability is one of the strongest arguments for reuse investment in drought-prone regions.

Sources

• European Environment Agency. (2025). Water Resources Across Europe: Confronting Water Stress in a Changing Climate. Copenhagen: EEA Publications.
• European Commission. (2020). Regulation (EU) 2020/741 on minimum requirements for water reuse. Official Journal of the European Union, L 177/32.
• Companyia d'Aigues de Sabadell. (2024). Sabadell Water Reclamation Project: First Year Performance Report. Sabadell: CASSA.
• SE|BS Stadtentwasserung Braunschweig. (2025). Agricultural Reuse Modernization: Annual Operations Summary 2024. Braunschweig: SE|BS.
• Thames Water. (2025). Beckton Water Recycling Plant: Commissioning and Early Operations Report. Reading: Thames Water Utilities.
• Drinking Water Inspectorate. (2024). Regulatory Framework for Indirect Potable Reuse in England. London: DWI.
• International Water Association. (2025). Global Water Reuse: Trends, Technologies, and Governance Frameworks. London: IWA Publishing.
• Agencia Catalana de l'Aigua. (2024). Drought Response and Water Reuse Strategy for Catalonia 2024-2030. Barcelona: ACA.