The project, in which Eawag researchers are working closely with local research partners and stakeholders, has shown that decentralised water reuse can be an effective solution for tackling water scarcity. However, this requires technological, regulatory, economic and social factors to work in tandem. Therefore, the study examined not only technical innovations but also issues of user acceptance, the legal framework and viable business models for the use of recycled water.

The project will run until summer 2026, but the highlight was a workshop involving all stakeholders, held this spring, where the results were reviewed and discussions took place on which elements need to work together to ensure that an innovative, safe and circular water management system can actually be established in a city like Bengaluru.

Unchecked population growth calls for innovative solutions

The backdrop to the discussion on recycled water is the city’s unchecked growth – one of the causes of water scarcity. The population grows by around half a million people every year. “If you have to expand the wastewater infrastructure every year to accommodate a city the size of Zurich,” says Christian Binz, “a decentralised approach offers many advantages.”

In Bengaluru, a law has been in place since 2015 that obliges large-scale property owners to treat their wastewater independently and reuse it locally. Yet, around 80 per cent of these decentralised WWTPs do not function satisfactorily. The reasons for this include not only problems with the technological design of the plants but also social barriers to adopting these innovations.

Technology: developing affordable, robust and reliable technologies

On a technical level, the WaterReuseLab has made important progress: following an evaluation of the currently installed technologies for decentralised wastewater treatment, the Eawag experts concluded that many of them do not consistently meet the quality criteria for safe reuse. A new approach is now being tested in the Eawag laboratories. It relies on a combination of membrane filters, affordable sensors and the use of AI. The goal is to develop a technology that is as cost-effective, robust and as easy to operate as possible. The modular system can be used as a containerised unit to supplement the existing facilities. This additional post-treatment is intended to ensure a consistent supply of high-quality recycled water. “Our experiences in Bengaluru inspired us to adopt this innovative approach,” emphasises Christian Binz. In collaboration with local companies, this approach shall be applied and tested in systems in Bengaluru.

Legal framework: enabling the sale of recycled water

In the area of recycled water regulation, the WaterReuseLab sought solutions for quality assurance and issues of accountability. The results of these investigations have been incorporated into a new law that has created a local market for treated wastewater. The background to this was a severe drought in 2024, which led to a water emergency. Many property management companies had to ask residents to vacate their buildings, as there was simply not enough water anymore. Residents refused to accept this and exerted political pressure. The message was clear: treated wastewater is too valuable to be left unused!

The WaterReuseLab played a crucial role in this situation. “The drought actually proved to be a real driver of innovation,” says Christian Binz. The local project partners, WELL Labs, were asked by the local government how water reuse could be better regulated by law. They fed insights and suggestions from the project into the political process, resulting in a new legal framework that allows property owners to resell treated wastewater within their local area.

Business models: creating a market for treated wastewater

Innovative solutions are also emerging in the design of potential business models for water reuse: for example, one property management company is already selling treated wastewater to a nearby laundry – and making a profit in the process. In other cases, buildings with their own WWTP supply recycled water to construction sites in the neighbourhood. Another outcome of this research is a new tool that supports residents in the planning of new treatment plants. It highlights potential benefits for property management companies when it comes to upgrading or replacing existing treatment plants in ways that allow for broader and high-quality water reuse options.

User acceptance: recycled water enjoys widespread support

As surveys of the local population have shown, people in the Bengaluru are highly receptive to various forms of recycled water. This even applies to drinking water recovered from wastewater. One possible reason could be that the population is keen to be prepared for future droughts. In two building complexes, drinking-quality water is already being recovered from wastewater.

A city on the cusp of a more sustainable water future

The WaterReuseLab has set things in motion in Bengaluru. “The project has led to a profound shift in thinking regarding the decentralised reuse of wastewater in the city,” says Satish Mallya, President of the Bangalore Apartments’ Federation. “It was the catalyst for a remarkable policy shift that allows residential complexes in the city to sell 50 per cent of their treated service water to third parties.” The Apartments’ Federation brings together property management companies that oversee housing for several million people in Bengaluru. The association is one of the WaterReuseLab’s key project partners.
 

The WaterReuseLab also scored another win: the project’s workshops succeeded in bringing together relevant stakeholders such as companies, property developers, public authorities and water suppliers. After the initial scepticism, these parties have now joined forces in a coalition that promotes decentralized water reuse.

One key question remains: Can the insights gained in Bengaluru be applied elsewhere in the world? Christian Binz: “If technical and social elements harmonise, then solutions from Bengaluru can indeed be transferred to other cities. Not just in India, but in many other places around the world – and perhaps even in Switzerland one day.”