Reverse osmosis is a water treatment process that forces water through an extremely fine membrane to remove dissolved minerals. Purified water passes through the membrane and collects in a storage container. Most of the dissolved minerals in the water cannot pass through the membrane and are flushed away as waste. Small household reverse osmosis systems flush from three to twenty litres of water to waste for every litre of treated water. This flushing helps maintain treated water quality and prevent fouling of the membrane.
Reverse osmosis competes directly in the marketplace with distillation. Both can provide small amounts of high quality water for drinking, automatic humidifiers, and watering plants. The diagram below shows the makeup of a typical household reverse osmosis unit.
Reverse osmosis mechanics – water passes first through a sediment filter, which culls coarse solids that could plug up the reverse osmosis membrane. Water next follows the spiral winding of the membrane. Contaminated water leaves the system and goes down the drain; treated water moves on to a holding tank. When water is drawn from the tank, it flows through a carbon filter which removes organic chemicals, then to a spigot.