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Just a year back, the city of Mumbai was battered with heavy rain during May-June. The India Meteorological Department issued intermittent yellow and orange alerts for heavy downpours. Cut to 2026, the city is complaining about water crisis due to late arrival of monsoon. The Brihanmumbai Municipal Corporation (BMC) manages the city’s water supply from the primary reservoirs: Bhatsa, Middle Vaitarna, Upper Vaitarna, Tansa, Lower Vaitarana, Vihar, and Tulsi. The reservoirs have dropped to around 10 per cent of their capacities, and the BMC has rolled out stringent measures to cut down the water supplies. The civic body has imposed a 10 per cent city-wide water cut and completely suspended water supply to all construction sites and swimming pools across Mumbai. Additionally, industrial, commercial, and sports club establishments are facing a 20 per cent cut as the city’s seven lakes have dropped to critically low levels.
Mumbai consumes around 4,000 million litres per day (MLD) of water according to the BMC. The water is sourced through seven distant lakes through 650 km of transmission lines and 6,000 km of service mains. The city experiences a shortfall of almost 565 MLD. The non-revenue water loss according to recent reports has risen to more than 30 per cent, compared to 20 per cent in 2009. The news reports say that more than 900 MLD of treated water is lost due to just leaks and illegal connections, which is much more than the demand-supply gap.
Initially, the picture was different for the metropolis. Piped water came to Mumbai in 1860 with the commissioning of the Vihar scheme on the Mithi river, then some 20 km north of the city. About 32 MLD was sourced from the scheme to cater to a population of only 0.7 million. Then in 1885, with water shortages striking the city, it was decided that Mumbai would go further upstream on the Mithi to develop the Tulsi Lake, followed by the Powai, as its water sources.
Since then, the city’s search for new sources has not stopped. After Tansa, which was commissioned in 1948, the city decided to tap the Vaitarna river some 175 km away. Now, the city is virtually dependent on these far-off reservoirs to meet its needs. More projects on desalination and Advanced Tertiary Treatment Plants (ATTP) have been planned to cater the population of 2041 where the demand-supply gap is expected to be 6,424 MLD according to the BMC’s Environment Status report of 2024-25.
To bridge the demand-supply gap, there are tankers which draw water from the city borewells. Moreover, slums in Mumbai where almost 40 per cent of its population resides, depend heavily on groundwater in absence of any pipelines. There is a huge dependence on borewells, community wells and tanker supplies even by the commercial hubs, construction sites and the gated colonies.
Mumbai’s rapid urbanisation—expanding at nearly 4 per cent annually—has paved over natural catchments and severely depleted the city’s historic water bodies. Concretisation prevents rainwater from infiltrating the soil, which results in chronically low groundwater recharge, heavy localised flooding, and high vulnerability to seawater intrusion and severe summer shortages.
According to the 2024 Maharashtra Pollution Control Board (MPCB) report, around 2,727 MLD capacity of sewage treatment plants (STPs) have been constructed under the Municipal Corporation of Greater Mumbai (MCGM). There are 8 STPs in total but the utilisation capacity according to this report is only 53 per cent.
Depending on the amount of water that is supplied, the sewage generated is 3200 MLD. Of this, around 1,452 MLD is treated which results in almost 1,748 MLD of sewage to flow into the nearby marshes, wetlands and creeks. The local river Mithi has been virtually killed. The river acts as open drain for 13 major nallahs: untreated domestic sewage & industrial effluents.
Crores of rupees have been pumped in to construct more than 2,400 MLD capacity of STPs according to the MPCB. As there is a huge utilisation of groundwater by big colonies and commercial centres, hence the amount of sewage generated in the city is much higher than what has been estimated by the thumb rule.
Mumbai now needs to focus on groundwater recharge and wetland revival: BMC was the first municipal corporation in Maharashtra to make Rooftop Water Harvesting (RWH) compulsory for new buildings under the Intimation of Disapproval (IOD) and as a prerequisite for Completion Certificate to buildings. RWH was made mandatory for buildings of more than 1,000 sq m in 2002, and the rule was amended to make RWH mandatory for buildings of more than 300 sq m in 2007. BMC even offers a 5 per cent property tax rebate to housing societies that successfully implement eco-friendly measures like RWH and vermiculture. BMC needs to scale up these initiatives through the existing the RWH cell. Citizens should be motivated to implement working systems with effective groundwater recharge systems. The cell should also move towards city level initiatives by restoring polluted water bodies’ catchment and abating pollution in the natural drains entering the water bodies. With an area of 437 sq km, the BMC area has a potential equivalent to 6 months of water supply to the city. Mumbai annually receives around 2,000 mm of rainfall and at the rate of water supply of 150 lpcd, the RWH potential of the city is around 437,000 million litres annually.
Reusing treated wastewater will also be a timely solution to prevent mixing of treated and untreated wastewater. While the ultimate goal under state policy is to reuse 30 per cent of this recycled water, widespread city-scale reuse is still developing. To transition towards comprehensive water security and reach the 30 per cent reuse goal, the BMC is piloting an ATTP pilot project at its existing facility in Colaba. This 12 MLD project focuses on treating secondary wastewater to potable standards. Currently, most of the treated wastewater is flowing into the creeks and wetlands.
The Centre for Science and Environment (CSE)’s “Waste to Worth” publication recognises the first well-documented instance of wastewater reuse in India is from Mumbai, where the textile industry in the year 1964-65 observed that about 15-20 per cent of the wastewater generated could be reused without any pre-treatment for certain applications like blanket washing, thereby reducing the costs. The recycling was carried out in as many as 22 mills of Mumbai and later, a few more industries started recycling. Mumbai’s Air India building was the first commercial building in India to treat blackwater generated from its toilets and reuse it as cooling water in centralised air conditioning systems. CSE’s research shows that currently, the majority of treated wastewater in Mumbai is discharged into the sea after ensuring it meets the required quality standards. The reuse possibility is limited because of Mumbai’s status as a coastal city. Due to its natural slope and terrain the infrastructural development of supplying treated water against the slope will be immensely challenging and cost-intensive. Hence, the sewerage operations department of MCGM has adopted a programme to decentralise wastewater treatment. The MCGM has made it mandatory for high-rise buildings to recycle and reuse wastewater, and to build an STP. Additionally, they are working on creating “Grey Water Recycle Bye-laws” to support the recycling and reuse program. As gated colonies and commercial centres are going for borewell extraction, hence implementing recycling-and-reuse for colonies, hotels and malls should be the need of the hour.
In 2024, India’s IT and tech capital of Bengaluru almost faced a day zero. The story was all about mismanagement of water sources. The story of Mumbai is no different. But there is ample scope to improve the situation. The huge potential lies both in rainwater harvesting and recycle and reuse of treated wastewater.