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How is reverse osmosis used to make seawater suitable for drinking?

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Diagram of a water treatment plant showing the process from water inlet through mixing, coagulation, flocculation, settling, filtering, chemical treatment with chlorine, storage, and high-lift pumping to the distribution system. — water purification Water from inlets located in the water supply, such as a lake, is sent to be mixed, coagulated, and flocculated and is then sent to the waterworks for purification by filtering and chemical treatment. After being treated, the water is pumped into water mains for storage or distribution.

Reverse osmosis is a desalination process used to produce potable water by removing dissolved salts and impurities from seawater.12

In a natural state, osmosis causes water to flow from a region of low concentration to one of high concentration across a semipermeable membrane. To reverse this, the process applies high hydrostatic pressure to the concentrated seawater, forcing the water molecules to move against the concentration gradient through a synthetic semipermeable membrane.134

This membrane acts as a selective barrier that allows fresh water to pass through while blocking larger molecules, such as dissolved ions and mineral salts. To maximize efficiency and conserve space, these membranes are typically packaged in multiple layers within long tubes. While the process is highly effective for water purification, it is energy-intensive and produces brine as a byproduct, which presents significant environmental challenges that must be managed to protect public health and ecosystems.132