Salt Questions · Science, chemistry & environment
How do desalination plants turn ocean water into drinking water?
Short answer
Most desalination plants use reverse osmosis: seawater is pumped at high pressure through membranes with pores so fine that water passes through but salt is left behind. Older and some Middle Eastern plants use thermal methods that boil seawater and condense the steam. Both need a lot of energy and produce concentrated brine as a by-product.
Reverse osmosis desalination
- 1Seawater in, pre-filtered
- 2High pressure through membranes
- 3Fresh water passes; salt is left behind
- 4Remineralised and disinfected for drinking
Reverse osmosis
- Seawater is screened and filtered to remove debris and particles.
- High-pressure pumps push it against semi-permeable membranes.
- Fresh water passes through; most of the salt stays behind in a concentrated stream.
- Minerals are added back and the water is disinfected for drinking.
Thermal desalination
Seawater is heated so water evaporates, then the vapour is condensed as fresh water. Multi-stage flash plants reuse heat across many chambers at decreasing pressure.
Challenges
- Energy: pushing water through membranes takes a lot of power.
- Brine: for every litre of fresh water, plants produce roughly a litre or more of concentrated brine, which must be disposed of carefully.
- Marine life: intakes can trap small organisms.
Related on The Salt Almanac
More science, chemistry & environment questions
- Why does salt dissolve faster in hot water than cold water?
- What is rock salt made of?
- How does salt water affect the density of water?
- Why do things float easier in the Dead Sea?
- What is the difference between organic and inorganic salt in chemistry?
- What is the chemical formula for table salt?
Cite this page
For school projects and reports. Teachers often prefer the original sources too: see the list below.
The Salt Almanac. (2026, November 8). How do desalination plants turn ocean water into drinking water. https://saltalmanac.com/answers/how-do-desalination-plants-turn-ocean-water-into-drinking-water
“How do desalination plants turn ocean water into drinking water.” The Salt Almanac, 8 Nov. 2026, saltalmanac.com/answers/how-do-desalination-plants-turn-ocean-water-into-drinking-water. Accessed [today's date].
“How do desalination plants turn ocean water into drinking water.” The Salt Almanac. Last modified November 8, 2026. https://saltalmanac.com/answers/how-do-desalination-plants-turn-ocean-water-into-drinking-water.
Original sources
- PBS NOVA. Why it's so hard to make salt water drinkable. https://www.pbs.org/wgbh/nova/article/seawater-desalination-reverse-osmosis-thermal
- Wikipedia. Desalination. https://en.wikipedia.org/wiki/Desalination
- Wikipedia. Reverse osmosis. https://en.wikipedia.org/wiki/Reverse_osmosis