Desalination in India: Technologies, Costs and Where It Makes Sense

Chennai has no perennial river, and in 2019 its reservoirs ran dry. Today, part of its answer comes from the sea. Chennai runs three desalination plants with 360 MLD of capacity, a 400 MLD plant is being built at Perur, and another 400 MLD plant has been announced at Minjur. Together, they will take the city close to 1,160 MLD of desalinated water.

Mumbai has awarded its first plant at Manori. Gujarat’s Dahej industrial belt already runs on seawater. Coastal states are now writing desalination into their long-term water plans.

But it is also the costliest way to make drinking water. So where does it actually make sense?

Why India Is Turning to the Sea

Seawater carries around 35,000 to 45,000 mg/L of dissolved salts. India's drinking water standard, IS 10500, accepts just 500 mg/L. Desalination closes that gap.

What utilities really pay for is reliability. A desalination plant delivers the same volume in a drought year as in a wet one. For coastal cities with exhausted sources, and for industries that states would rather not supply from rivers and canals, that certainty is worth a premium.

Also Read: What Is Integrated Water Management and Why Does It Matter?

The Desalination Process, Simplified

Almost every large plant in India uses seawater reverse osmosis (SWRO). Here is the journey from sea to tap:

1. Intake. Large pipelines draw seawater from offshore. At Perur, two 2,500 mm pipelines run about 10 metres below the sea.
2. Pre-treatment. Dissolved air flotation, dual media filters, and often ultrafiltration remove algae, silt, and organics. This is where good plants and struggling plants part ways.
3. High-pressure pumping. Pumps push water to roughly 55 to 70 bar. Energy recovery devices reclaim much of that energy from the outgoing brine.
4. Reverse osmosis. Membranes let water through and hold salt back. At Nemmeli, TDS drops from about 40,000 ppm to around 300 ppm.
5. Remineralisation and disinfection. Minerals are added back so the water tastes right and doesn't corrode pipes, then it is chlorinated.
6. Brine discharge. Concentrated brine returns to the sea through diffusers that dilute it quickly.

Then comes the step people forget: Perur's water will travel through a 59 km main before reaching consumers.

Desalination Technologies Used in India

LTTD, developed by the National Institute of Ocean Technology, uses the temperature difference between warm surface water and cold deep-sea water near Lakshadweep.

Where Desalination Plants in India Stand Today

Tamil Nadu leads by a wide margin. Minjur (100 MLD) opened in 2010, followed by Nemmeli I and the 150 MLD Nemmeli II. Perur, funded largely by JICA and run on a 20-year design, build and operate model, will be the largest desalination plant in South Asia, with completion expected in 2027.

Industry has moved fast too. The 100 MLD Dahej plant has supplied Gujarat's petrochemical cluster since 2022, and a 60 MLD plant for SIPCOT's industrial parks was contracted in 2026. Mumbai's 200 MLD Manori plant, expandable to 400 MLD, was awarded in December 2025 after four unsuccessful tender rounds.

Desalination Cost: What You Are Really Paying For

Desalination cost has two layers.

Capital cost. Nemmeli cost about Rs 533 crore for 100 MLD in 2013. Perur's estimate has grown from about Rs 4,276 crore to roughly Rs 6,000 crore, including marine works, conveyance, and long-term operation. Chennai Metrowater data puts the capital cost per MLD at about double that of a conventional treatment plant.

Operating cost. Indian plants have reported roughly Rs 30 to Rs 70 per kilolitre. Chennai Metrowater agreed to buy Minjur's water at Rs 48.66 per kilolitre, while Nemmeli's production cost was estimated at Rs 30 to 42.

What drives these numbers?

• Energy, the single biggest operating expense
• Membranes and chemicals, which climb fast if pre-treatment is weak
• Marine works and pipelines to and from the sea and city
• Utilisation, since a half-used plant still carries most of its fixed costs

Desalinated water isn't cheap water. It is dependable water.

Where Desalination Makes Sense, and Where It Doesn't

It makes sense for:

• Coastal metros like Chennai with unreliable surface sources
• Coastal industrial clusters that need steady, large volumes
• Islands and remote coastal settlements
• Saline groundwater belts, using small brackish water plants

Other options usually come first when:

• The city is far inland, where pumping costs can outweigh the plant itself
• The network is leaking. Indian utilities lose around 38% of treated water, and fixing that is far cheaper than making new water. See how District Metered Areas cut NRW.
• Treated wastewater can serve industry at a lower cost
• Lakes, tanks, and recharge structures are still untapped

Even the best plant depends on what surrounds it: renewable energy to cut power bills, efficient pipeline networks to move water, and 24x7 supply systems that don’t waste it, efficient pipeline networks to move water, and 24x7 urban water supply systems that don't waste it.

SPML on the Perur Project

SPML Infra, in a joint venture with JWIL Infra, is delivering the Rs 258 crore CP2 package of Chennai's Perur desalination project for CMWSSB. The scope covers pumping stations at Perur (400 MLD) and Porur (350 MLD), a 15 ML ground level reservoir at Porur, pipeline works, flow metering, and 20 years of O&M. In short, it is the link that carries desalinated water from the coast into Chennai's network.

Conclusion

The desalination process is proven. The real question is fit. For coastal cities, industries, and islands that have run out of cheaper reliable options, a desalination plant offers something rare: the same volume of safe water every day, rain or no rain. Everywhere else, fixing losses and reusing water should come first.

SPML Infra delivers end-to-end EPC solutions across the entire water cycle. Explore our water infrastructure solutions or request a project consultation.

FAQs

What is desalination in simple words?

It is the removal of salt from seawater or brackish groundwater to make it fit for drinking or industrial use.

Which is the largest desalination plant in India?

The 400 MLD Perur plant near Chennai, now under construction. Among operating plants, Nemmeli II (150 MLD) is the largest.

What is the desalination cost in India?

Large seawater plants have reported operating costs of roughly Rs 30 to Rs 70 per kilolitre, or about 3 to 7 paise per litre.

Which technology is most used for desalination in India?

Reverse osmosis, used in nearly all large municipal and industrial plants.

Is desalinated water safe to drink?

Yes. It is remineralised and disinfected to meet IS 10500 standards before supply.