Bengaluru, one of India’s fastest-growing megacities, is battling a severe water crisis, but a recently published study reveals that recycling wastewater directly within apartment complexes could provide a massive lifeline. An international team of researchers, including those from the Swiss Federal Institute of Aquatic Science and Technology, Switzerland, Georgetown University, USA, and Water, Environment, Land and Livelihoods (WELL) Labs, Bengaluru, has discovered that treating and reusing wastewater locally could safely recycle up to 60% of the city's sewage.
To understand where the system currently falls short, the team investigated Bengaluru’s complex web of water laws and real-world practices. The team conducted their research by reviewing two decades of urban water policies and interviewing a wide range of people, from government officials to everyday residents. They combined this with quantitative estimates of water demand and physical inspections of 22 decentralised sewage treatment plants, mostly located in residential buildings.
Unlike traditional city planning, which relies on a single massive treatment facility and water pumped from distant rivers, decentralised systems operate on a neighbourhood scale. Wastewater generated from sinks, showers, and toilets is treated right inside the building using physical, biological, and chemical processes. The cleaned water is then pumped back for non-drinking purposes, such as flushing toilets, watering gardens, mixing concrete for construction, and cooling commercial buildings. This local loop forms a circular water economy, dramatically reducing the need to extract fresh groundwater.
The researchers estimate that between 25% and 60% of all wastewater generated in Bengaluru (between 473 and 1187 million litres per day, or MLD) could be safely reused for non-potable purposes like toilet flushing, landscaping, and construction. However, despite having the world’s highest concentration of decentralised sewage treatment plants (over 3,000 predominantly in residential complexes), only about 47 MLD of treated wastewater from these local sources is currently being reused.
During site visits, the researchers observed a massive gap between policy mandates and on-the-ground reality. Over 80% of the visited treatment plants failed to implement reuse for all possible non-potable purposes as mandated by law. Over 80% of the facilities exhibited operational compliance issues, resulting in poor water quality characterised by noticeable colour, odour, and turbidity. More than 80% of the sites lacked trained personnel. Complex treatment plants were often operated by untrained security guards or housekeeping staff, leading to inefficiencies and system failures.
The researchers also found that many government rules were implemented in a top-down manner without stakeholder input and were scientifically or logistically unrealistic. For example, a previous mandate requiring Zero Liquid Discharge (100% onsite reuse) was deemed unfeasible for existing buildings and was rolled back to a 50% mandate. The researchers also point out that roles and responsibilities are scattered across various government, environmental, and water boards, leading to poor coordination and ineffective enforcement.
Treated wastewater also struggles to compete economically because piped city water is heavily subsidised, and groundwater is often extracted unsustainably for virtually no cost. Because water from the public utility is incredibly cheap, users have little financial incentive to maintain their decentralised treatment plants or buy recycled water.
As climate change and rapid urbanisation drain freshwater resources worldwide, cities can no longer rely solely on pumping water from distant lakes or on rapidly depleting underground aquifers. By highlighting the urgent need for cohesive laws, clear public health standards, and government support for local water recycling, this work provides a roadmap for other thirsty megacities. Implementing these local, circular water systems effectively can ultimately secure a sustainable, climate-resilient water future for millions of urban residents worldwide.
