The sea is a very large body of cool water, and it can absorb heat. In seawater cooling, cool water is pumped from the sea through a heat exchanger, where it takes heat from a separate, sealed loop of freshwater that serves the data centre. The two never mix. The warmed seawater then goes back to the sea. Because the heat goes into the sea rather than into the air by evaporation, the data centre needs far less freshwater for cooling. The challenges are engineering ones: salt corrodes metal, sea life grows on surfaces, and the returning water must not harm the marine environment.
How it works
A study for the State of Hawaii in 2002 describes the design for cooling buildings with seawater: a pipe brings cold seawater to a heat exchanger at the shoreline, which cools a closed cycle fresh water distribution system serving the buildings. The heat exchanger has to be resistant to corrosion by seawater. The same study notes that the approach greatly reduces the water and toxic chemical use and disposal associated with cooling towers. Its figures are for district cooling of buildings, not data centres, but the principle is the same.
| Part | What it does |
|---|---|
| Intake | Draws cool seawater, ideally from deeper, colder water, through screens |
| Heat exchanger | Passes heat from the freshwater loop to the seawater without the two mixing |
| Freshwater loop | Carries heat from the data centre halls to the heat exchanger, sealed and reused |
| Return | Sends the warmed seawater back to the sea, at a depth and place chosen to protect marine life |
A working example
Google says its data centre in Hamina, Finland, uses a cooling system with seawater from the Bay of Finland. The site is a former paper mill that Google bought in 2009, and the data centre opened in 2011. Google also reports an offsite heat recovery project with the local energy company, using heat from the data centre to warm homes and businesses.
The engineering challenges
Seawater is hard on equipment. Research recorded by the US Department of Energy used corrosion-resistant materials (titanium and AL-6X stainless steel) in marine heat exchangers, and tested low levels of chlorination, in the range of 25 to 70 parts per billion, to control the growth of marine organisms on surfaces, known as biofouling. Tests using deep, cold water showed negligible biofouling for an extended period of time. Intakes also need screens and low flow speeds so that fish are not drawn in, and the warm return water needs careful design. The companion article on marine life explains how those effects are assessed.
What is not certain
- Most public figures on seawater cooling come from building cooling projects. Data centre results depend on the site, the depth of cool water and the climate.
- Not every coast has cool water close to shore. Shallow, warm coastal water cools less well.
- Approvals for intakes and discharges depend on national and local environmental rules.
Sources and method
- State of Hawaii, Department of Business, Economic Development and Tourism, with Makai Ocean Engineering and the University of Hawaii, Sea Water District Cooling Feasibility Analysis for the State of Hawaii, October 2002. https://energy.hawaii.gov/wp-content/uploads/2011/10/SeaWaterDistrictCoolingFeasibilityAnalysisfortheStateofHawaii2002.pdf
- Google, Hamina, Finland data centre page. Read 29 October 2026. https://datacenters.google/locations/hamina-finland/
- US Department of Energy, Office of Scientific and Technical Information, Biofouling control for marine heat exchangers using intermittent chlorination, research record CONF-840816-11. https://www.osti.gov/biblio/7075894
Method: each link was opened on 29 October 2026 and every figure was taken from the page cited beside it. No figure was estimated.
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This article provides general information, not investment advice or an offer of securities.