Published on The Water Blog

Rethinking wastewater: Chennai’s journey towards water security

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Plastic buckets filled with water on a roadside in Chennai, India. Plastic buckets filled with water on a roadside in Chennai, India.

Chennai, a city on the southeastern coast of India and the state capital of Tamil Nadu, has one of the India’s fastest-growing urban economies1. The region is the nation’s automotive hub and home to several other manufacturing industries ranging from petrochemicals to electronic hardware, textiles, and apparel. Urbanization and economic growth, over the last two decades have seen Chennai’s population increase 1.5 times, making it the fourth-largest city in India with over 10 million people.

Chennai historically relied on rainfed lakes with a combined storage capacity of about 11,000 million cubic feet, supplemented with groundwater that provided up to an additional 120 million liters of water per day (MLD). However, the demand for water in the city has increased more than 50% over the past ten years due to industrial development, increasing population, and larger per capita needs triggered by economic growth and lifestyles.

In the past two decades, Chennai has also experienced extreme weather patterns: floods in 2005, 2010, and 2015, bookended by droughts in 2003–04 and 2016–18 . And since the city is entirely dependent on rains for recharging its water resources, monsoon failures lead to acute water scarcity. In 2019, the city reached “Day Zero” or the day when reservoirs had run dry, and no water was left. 

To protect against the vagaries of nature, build resilience to climate change, and increase water availability, the Chennai Metropolitan Water Supply and Sewerage Board (CMWSSB) is working to diversify water supply through desalination and sewage treatment reuse. Chennai mandated rainwater harvesting and became the first city in India to reuse 10 percent of collected wastewater, with plans to achieve a reuse rate of 75 percent. 

Between 2015 and 2019, the CMWSSB established two tertiary treatment plants, one of which was financed under the World Bank financed Tamil Nadu Sustainable Urban Development Program to supply high-quality treated wastewater via a grid to industries in and around Chennai. This targeted supply to industries ensured uninterrupted availability of water; and brings in revenue to the utility to sustain their sewage treatment operations. The equivalent “freed” freshwater capacity (hitherto supplied to industries) is now rerouted for domestic water use in the city. CMWSSB is also recovering energy from wastewater in more than half of its wastewater treatment plants and exploring to sell most of the biosolids generated as manure for application to agricultural land.

Having met the water supply needs of industries and learning from the experience of the Indian Institute of Technology that has been operating an indirect potable reuse plant for several years, CMWSSB decided to pilot two plants each with a capacity of 10 MLD for indirect potable reuse and thereafter scale up to 260 MLD to meet the growing water demand. The proposed process has several advantages including the availability of critical infrastructure, cost-effectiveness as compared to other options to augment water supply and more importantly having a higher climate resilience to ensure water security. By 2024, the Chennai water utility plans to complete indirect potable reuse plants with installed capacity of 260 MLD. Together with infrastructure creation, CMWSSB should focus on outreach program to get public acceptance for the planned reuse efforts. When completed these reuse efforts will help CMWSSB add about a quarter of the city’s water demand, diversify water supply sources and contribute towards building urban resilience and water security.

1Recent estimates of the economy of the Chennai Metropolitan Area have ranged from US$79 million to US$86 billion (purchasing power parity [PPP] gross domestic product [GDP]), ranking it as the fourth- to sixth-most-productive metropolitan area of India.


Ravikumar Joseph

Senior Water and Sanitation Specialist

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