The City of 1000 Tanks: How a nature-inspired water solution promises scalability, sustainability

The 97-year-old Little Flower Convent—a school for 500 visually and hearing-impaired children in Chennai—recently became a centre for City of 1000 Tanks, an innovative programme based on nature-inspired water conservation and established through the Water as Leverage (WaL) method.  

WaL—a programme spanning India, Indonesia, and Bangladesh—is a methodology developed by the Netherlands government with international partners. 

It has recognised that a result-driven, holistic, and inclusive project preparation approach is the best way to create scalable and sustainable solutions for urban climate adaptation challenges.

A growing global community of governments, cities, communities, designers, engineers, NGOs, and researchers use this methodology to develop solutions for complex water challenges in urban regions.

Last week, The City of 1000 Tanks’ Water Balance Project was completed by Henk Ovink, the First Special Envoy for International Water Affairs for the Kingdom of the Netherlands. 

The project—funded by the Netherlands government in partnership with the city of Chennai, UN-Habitat and Resilience Cities Network, and supported by the UN high-level panel on water, among others—demonstrated a model for the city to become water secure. 

Broadly, the process involves harvesting rainwater and treating wastewater before releasing it into the underground aquifer through infiltration gardens.

“Chennai has a problem that can be defined as uncertainty when it comes to water. Either there is too much of it or too little of it,” says Jayashree Vencatesan, Ecologist and Managing Trustee of Care Earth Trust—one of the NGOs behind the initiative. 

She adds, “Climate-related disasters are slowly but steadily creeping into Chennai. It’s almost like two sides of a coin—the recurrent flooding that the city experiences followed by severe droughts.” 

The programme has experts from urban design, water management, social and cultural engagement, and policy and finance sectors. The team is led by OOZE Architects, in collaboration with Madras Terrace, IIT Madras, Care Earth Trust, Paperman Foundation, Biomatrix, Pitchandikulam   Forest Consultants, The Rain Centre, IRCDUC, Urayugal Social Welfare Trust, and The Goethe Institute. 

This multidisciplinary team observed three key challenges at the Little Flower Convent—sewage overflow, floods during monsoons, and drought during summer months. 

“It seems to reflect the kind of problems the city has on a much larger scale. Therefore, we thought, if we can solve the problem of water here, then we can use it as a demonstration model to scale up in other parts of the city,” a representative from the Tamil Nadu Urban Habitat Development Board tells SocialStory.

Over the last two years, the project has treated 27,500 litres of water per day, generated by wastewater collected from 300 residents. It is treated through two underground anaerobic tanks rich with micro-organisms that work on the wastewater to achieve 80% of treatment capacity. 

This water is passed through constructed wetlands with halophytic plants that enable aerobic treatment. The entire process is natural and solar-powered.

“The pilot project at Little Flower Convent is a first demonstration that will achieve its full potential when replicated in institutions across the city. In parallel, we plan to scale it up through a flagship project in Mylapore,” says Eva Pfannes, Director of Ooze Architects and Urbanists and Team Lead of City of 1000 Tanks. 

“It is a vivid demonstration of the efficacy of scalable ecosystem-based adaptation tools that can be deployed to address similar issues in the city. Infiltration gardens, when implemented city-wide, will transform Chennai into a permeable and cool city. It will increase the capacity to absorb and recharge water, reducing the impact of flooding,” she adds. 

The team will continuously monitor the performance of this project by using embedded electromagnetic and electrostatic sensors. It will also measure the precise volume of the water treated against the impact on the groundwater level. 

Meanwhile, it will conduct regular tests to ensure the consistency of the quality of treatment, and the project beneficiaries will study the collected data to monitor the performance of the system live by smartphone. 

Further, the team will use the data sets to demonstrate efficacy and support capacity-building activities to implement solutions across Chennai. 

The team now aims to rope in the Chennai Metropolitan Water Supply and Sewerage Board and the Greater Chennai Corporation and also involve resident welfare associations, vulnerable communities, CSR partnerships, and institutions in the project.

“The  Water Balance Project shows that WaL is a game-changer. This people-centred and community-led solution could be applied to the world’s most pressing water challenges,” says Ovink. 

“The pioneer project in Chennai proves that the value of community-led, nature-based solutions can lead the way ahead for upscaling and replicating—spreading from the city and the Ganga basin to the world,” Ovink adds.