The wastewater exits the facility at around 20°C before being discharged into the sea. By using heat pumps to upgrade that residual energy and feed it into local heating networks, the city hopes to reduce reliance on gas while using infrastructure that already exists beneath the urban landscape.
Known as aquathermie, the approach is gaining momentum across the Netherlands as a way to capture and store thermal energy from surface water, wastewater, and drinking water systems. Unlike intermittent renewables like solar and wind, heat from wastewater offers a steady year-round supply, with the potential for seasonal storage underground to manage demand swings between summer and winter.
While it’s not intended to replace other renewables, aquathermal energy could become a key part of The Hague’s low-carbon heat strategy—one that focuses on local, circular sources of energy that align with the city’s spatial and infrastructure constraints.
Although the energy source itself is steady and local, the path to implementation is complex. Capturing heat from wastewater requires the installation of technical systems—heat exchangers, pumping stations, and connections to district heating grids—in a dense urban environment with limited space.
The study prioritizes spatial analysis to identify viable sites for system integration. It looks at which segments of the pipeline offer the most efficient heat recovery, where infrastructure can realistically be installed, and how to align this with neighborhood development timelines and existing heating systems.
Researchers are also evaluating which city districts offer the best fit for aquathermal deployment based on building density, renovation readiness, and compatibility with district heating. Neighborhoods like Vruchtenbuurt are already involved through initiatives such as “Warm in de Wijk,” helping inform both the technical and social dimensions of the project.
Although full-scale implementation wouldn’t happen before 2030, The Hague already has a working example: a sports facility launched in 2024 that uses heat from sewage water to cut gas consumption by over 170,000 cubic meters annually.
The collaboration with Delfland underscores a broader trend in climate infrastructure—one that blends water management, energy transition, and spatial planning into integrated regional solutions. For cities navigating the heat decarbonization puzzle, wastewater may be less waste and more overlooked asset.
