<P> Boiler water is the liquid phase of steam within a boiler . The term may also be applied to raw water intended for use in boilers, treated boiler feedwater, steam condensate being returned to a boiler, or boiler blowdown being removed from a boiler . </P> <P> Impurities in water will leave solid deposits as steam evaporates . These solid deposits thermally insulate heat exchange surfaces initially decreasing the rate of steam generation, and potentially causing boiler metals to reach failure temperatures . Boiler explosions were not uncommon until surviving boiler operators learned how to periodically clean their boilers . Some solids could be removed by cooling the boiler so differential thermal expansion caused brittle crystalline solids to crack and flake off metal boiler surfaces . Other solids were removed by acid washing or mechanical scouring . Various rates of boiler blowdown could reduce the frequency of cleaning, but efficient operation and maintenance of individual boilers was determined by trial and error until chemists devised means of measuring and adjusting water quality to minimize cleaning requirements . </P> <P> Boiler water treatment is a type of industrial water treatment focused on removal or chemical modification of substances potentially damaging to the boiler . Varying types of treatment are used at different locations to avoid scale, corrosion, or foaming . External treatment of raw water supplies intended for use within a boiler is focused on removal of impurities before they reach the boiler . Internal treatment within the boiler is focused on limiting the tendency of water to dissolve the boiler, and maintaining impurities in forms least likely to cause trouble before they can be removed from the boiler in boiler blowdown . </P> <P> At the elevated temperatures and pressures within a boiler, water exhibits different physical and chemical properties than those observed at room temperature and atmospheric pressure . Chemicals may be added to maintain pH levels minimizing water solubility of boiler materials while allowing efficient action of other chemicals added to prevent foaming, to consume oxygen before it corrodes the boiler, to precipitate dissolved solids before they form scale on steam - generating surfaces, and to remove those precipitates from the vicinity of the steam - generating surfaces . </P>

What is the purpose of boiler water treatment