A reverse osmosis plant is a manufacturing plant where the process of reverse osmosis takes place. Reverse osmosis is a common process to purify or desalinate contaminated water by forcing water through a membrane. Water produced by reverse osmosis may be used for a variety of purposes, including desalination, wastewater treatment, concentration of contaminants, and the reclamation of dissolved minerals. An average modern reverse osmosis plant needs six kilowatt-hours of electricity to desalinate one cubic metre of water. The process also results in an amount of salty briny waste. The challenge for these plants is to find ways to reduce energy consumption, use sustainable energy sources, improve the process of desalination and to innovate in the area of waste management to deal with the waste. Self-contained water treatment plants using reverse osmosis, called reverse osmosis water purification units, are normally used in a military context.

Reverse osmosis plants require a variety of pre-treatment techniques including softening, dechlorination, and anti-scalent treatment. Following pre-treatment, high levels of pressure send water through a semi-permeable membrane, which retains all contaminants but lets pure water pass through. Energy requirements depend on the concentration of salts and contaminants in the influent water; higher concentrations requires more energy to treat.