As Water Demand Rises, Mumbai Now Turns to the Sea for Drinking Water

Mumbai could soon turn to the sea to meet a growing share of its drinking-water needs. By 2029, the city is expected to receive up to 400 million litres of drinking water a day from a major desalination facility being developed at Manori in northwestern Mumbai.

The project would make Mumbai only the second Indian city after Chennai to produce drinking water from seawater on such a large scale. Once both phases are operational, the facility is expected to become India's largest desalination plant in terms of capacity.

Desalination plan dates back to Mumbai's 2009 water crisis

The idea of using seawater as an alternative source of drinking water gained serious attention after Mumbai's severe water shortage in 2009. The crisis resulted in daily water cuts across the city and highlighted the risks of relying almost entirely on rainfall and reservoirs.

The Brihanmumbai Municipal Corporation (BMC) subsequently explored desalination as a way to diversify Mumbai's water sources and reduce its dependence on the monsoon.

Years later, the plan has moved into the implementation stage. The BMC is developing the Rs 4,007-crore Manori desalination project, located along the city's northwestern coastline near Malad.

How will the desalination process work?

The plant will use desalination technology to separate freshwater from seawater by removing dissolved salts and other contaminants.

The process broadly involves:

• Seawater being pumped into the facility through dedicated intake systems.
• Initial filtration removing sand, seaweed and other solid material.
• High-pressure systems forcing the filtered water through semi-permeable membranes.
• The membranes allowing water molecules through while retaining salts and other dissolved substances.
• Essential minerals being added back to the treated water before it is supplied for consumption.
• Concentrated salty water, known as brine, being discharged into the sea under environmental safeguards.

Advances in membrane technology have helped bring down operating costs over the years. Improvements in energy efficiency, membrane life and water flow have also made large-scale desalination increasingly practical.

What is the capacity of the Manori project?

The facility will occupy around 12 acres at Manori.

Israel-based IDE Technologies will be responsible for constructing the desalination system and operating it for 20 years. Hyderabad-based GVPR Engineers will handle the project's civil construction and related infrastructure.

The first stage is designed to produce 200 MLD of drinking water. If the second phase is taken up within the proposed timeline, the plant's overall capacity could eventually reach 400 MLD, with the full capacity potentially being available by around mid-2030.

The project received coastal-zone clearances from state and central authorities in April. The approvals include a number of environmental conditions covering brine management, protection of the surrounding ecosystem, construction of offshore pipelines through tunnelling and the use of renewable energy to meet part of the plant's high electricity demand.

BMC Additional Municipal Commissioner Abhijit Bangar said construction work is expected to begin after the monsoon.

Why Mumbai is looking for alternative water sources

Mumbai's water requirement has been steadily increasing, putting additional pressure on the city's existing supply system.

The city currently receives around 4,100 MLD of water from its seven lakes and reservoirs. According to BMC estimates, however, daily demand is approximately 4,664 MLD, creating a deficit of roughly 500-600 MLD.

The shortage can become more severe when rainfall is delayed or the monsoon performs below expectations. Since Mumbai's reservoirs depend heavily on monsoon rainfall for replenishment, a weak rainy season can quickly raise concerns about water availability.

Earlier this year, reservoir levels dropped significantly, prompting the civic body to impose a 10% water cut across the city. The delayed onset of the monsoon added to concerns over whether the existing stock would last until substantial rainfall arrived.

With Mumbai's population, residential needs and commercial activity continuing to expand, demand for water is expected to rise further.

The Manori desalination project is therefore being positioned as a long-term effort to create an additional and more reliable source of drinking water — one that does not depend directly on the success or failure of the annual monsoon.