A reverse osmosis water filter, such as those connected to filter taps installed under the sink, countertop RO systems and some water cooling systems is a somewhat unique approach to water filtration that turns traditional approaches on their head.
Most traditional water filters work using osmosis, which is the movement of water molecules from a higher concentration solution to a lower one using a partially permeable membrane.
This is the process plants use to draw water from the soil into its roots as well as being part of other biological processes.
Reverse osmosis works in the opposite direction, where a solution with a lower concentration of water is moved across a partially permeable membrane to a higher concentration, often using some form of pressure.
This works when the water molecules are smaller than the other molecules dissolved in the water, such as salts, sugars and metals.
Unlike osmosis, where the final product would be an equal concentration between both sides of the membrane, reverse osmosis produces purified drinking water with a solution of impurities as a byproduct.
It is a highly efficient way to produce purified water from seawater, wastewater and other sources that is safe to drink, filtering out salt, organic contaminants, pathogens and metals from natural water sources.
In some industries, the process is used for the opposite reason; by filtering out the water you are left with a purer version of a solution, which is part of the process used to make maple syrup, concentrated milk and pure ethanol.
Typically, reverse osmosis removes bacteria, viruses, metals such as lead, chloride and sodium, and can also filter out magnesium, calcium and potassium, with other stages in the purification process such as carbon cartridges and ultraviolet light removing the rest.
Reverse osmosis is one of the most effective methods for water purification and is widely used in water treatment facilities to ensure that clean, safe drinking supplies are available to everyone.