Mumbai turns to seawater as rising demand widens water gap

For a city surrounded by the Arabian Sea, Mumbai's answer to its growing water crisis may increasingly lie in the waters that have long defined its landscape.

By 2029, Mumbai is expected to begin receiving desalinated drinking water from one of India's largest such projects, as the city looks beyond its traditional dependence on lakes, reservoirs and the monsoon to meet rising demand.

The Brihanmumbai Municipal Corporation (BMC) is building a ₹4,007-crore desalination plant at Manori, a coastal village near Malad in northwestern Mumbai. Once both phases are completed, the facility is expected to produce up to 400 million litres per day (MLD) of drinking water, potentially making it India's largest desalination plant by capacity.

For Mumbai, the project represents the culmination of an idea that has been discussed for more than 15 years.

The city first seriously explored desalination after the severe water shortage of 2009, when residents faced daily water cuts. The proposal was aimed at reducing Mumbai's dependence on rainfall and creating an additional source of water that would not be entirely at the mercy of the monsoon.

While Gulf countries and Israel have relied on desalination for decades, Mumbai's journey from considering the technology to building a large-scale facility has been slow.

Now, that long-discussed solution is finally taking shape.

How desalination can turn seawater into drinking water

Desalination works by removing dissolved salts and other impurities from seawater, producing water that can be treated and made suitable for human consumption.

At the Manori plant, the process will broadly involve several stages.

Seawater will first be drawn into the facility through intake pipes and filtered to remove sand, seaweed and other debris. The filtered water will then be pushed at very high pressure through specialised semi-permeable membranes.

These membranes allow water molecules to pass through while blocking dissolved salts and other impurities.

The treated water will then undergo further processing, including the addition of essential minerals, before it is made suitable for drinking.

The process also produces highly concentrated salty water known as brine. Its disposal is one of the key environmental concerns associated with desalination, and the Manori project has been given clearances with safeguards governing its discharge into the sea.

Advances in technology have helped make desalination increasingly viable. Falling membrane costs, along with improvements in efficiency, durability and water flow, have reduced some of the technological and financial barriers that once limited large-scale adoption.

Manori project to be built in two phases

Spread across 12 acres, the Manori facility will be developed in phases.

The first phase will have a capacity of 200 MLD. Israel-based IDE Technologies will construct the desalination system and operate the plant for 20 years, while Hyderabad-based GVPR Engineers will undertake the civil infrastructure.

According to a senior civic official, if the second phase is commissioned within the next six months, the plant's total capacity could eventually reach 400 MLD by mid-2030.

The project received coastal zone clearances from state and national authorities in April. The approvals came with a series of conditions designed to limit the project's environmental impact.

These include safeguards for brine disposal, measures to protect the local environment, tunnelling for offshore pipelines and the use of renewable energy to meet part of the plant's substantial power requirements.

"The work will start post-monsoon," said Abhijit Bangar, Additional Municipal Commissioner, BMC.

A widening water gap

The urgency behind the project is rooted in a simple problem: Mumbai needs more water than its existing sources can reliably provide.

The city currently draws around 4,100 MLD from its seven lakes and reservoirs. The BMC estimates that daily demand stands at around 4,664 MLD, leaving a shortfall of nearly 500-600 MLD.

That deficit can become particularly concerning when the monsoon arrives late or rainfall falls below normal.

Mumbai's reservoirs depend heavily on seasonal rains for replenishment. A weak monsoon can therefore quickly turn into a water-management challenge for a city where millions of people depend on a vast and tightly stretched supply network.

This year, reservoir levels fell to around 23.5 per cent of the city's annual requirement, prompting the BMC to impose a 10 per cent water cut across Mumbai. The delayed arrival of the monsoon intensified fears of a possible shortage before rainfall eventually brought relief.

But the underlying challenge remains.

Mumbai's population density, economic activity and expanding urban demands are placing increasing pressure on its existing water infrastructure. As demand rises, relying solely on rainfall-fed reservoirs could leave the city increasingly exposed to unpredictable weather patterns.

Looking beyond the monsoon

Desalination will not replace Mumbai's existing lakes and reservoirs. Instead, it is being positioned as an additional source of water that can provide greater resilience when traditional supplies come under pressure.

The scale of the Manori project reflects that changing approach.

For decades, Mumbai's water security has been closely tied to the monsoon. The city has depended on seasonal rainfall to fill reservoirs and sustain its water network through the year.

The new plant offers a different proposition: water from the sea, available regardless of whether the monsoon performs as expected.

If the Manori facility reaches its planned 400 MLD capacity, it could provide a significant addition to Mumbai's daily supply and help narrow the gap between demand and availability.

For a city whose identity, economy and geography have always been intertwined with the sea, Mumbai is now looking to the same sea for something it has always needed most — water.