Lime softening (also known as lime buttering, lime-soda treatment, or Clark's process)[1] is a type of water treatment used for water softening, which uses the addition of limewater (calcium hydroxide) to remove hardness (deposits of calcium and magnesium salts) by precipitation.
The process is also effective at removing a variety of microorganisms and dissolved organic matter by flocculation.
Lime softening provides soft water that can, in some cases, be used more effectively for heat transfer and various other industrial uses.
Lime softening is now often combined with newer membrane processes to reduce waste streams.
Lime softening produces large volumes of a mixture of calcium carbonate and magnesium hydroxide in a very finely divided white precipitate which may also contain some organic matter flocculated out of the raw water.