Reverse Osmosis is commonly used in desalination and waste-water treatment. It is finding increasing use in the treatment of brewing liquor and in low-pressure boiler feed water.

Unlike demineralisation, it has the advantage of not using acid or alkali regenerants but it does have the disadvantage of a reject stream which can be typically 25% of the feed water. Unless this water can be re-used, it can add to the cost of the total plant operation.