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How does reverse osmosis remove dissolved substances from water?

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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 water purification technique that removes dissolved substances by using hydrostatic pressure to force water through a semipermeable membrane.

In a natural state, osmosis causes water to flow from a region of low solute concentration to one of high concentration to equalize them. Reverse osmosis reverses this process by applying high pressure to the concentrated side, forcing the water molecules to diffuse through the membrane while leaving behind larger molecules and dissolved inorganic compounds, such as salts and other impurities.12

Because the membrane acts as a physical barrier that allows only small solvent components to pass, this method is highly effective for desalinizing seawater, treating brackish water, and processing municipal or industrial wastewater. It serves as a critical tool in ensuring public health by providing a reliable means to produce clean, safe drinking water.123