The purposes of water treatment in a marine steam power plant are to prevent damage to boilers, steam-operated equipment, and steam and condensate lives, and to keep all equipment operating at the highest level of efficiency. This laboratory exercise is designed to provide students with experiences in making accurate boiler water tests and to provide expertise they will be expected to apply during cadet shipping and in future maritime employment. The exercise consists of four procedures, applicable to samples of water drawn from any source. These include: (1) total alkaalinity "A" reading; (2) chloride test; (salinity); (3) caustic alkalinity "B" reading; (4) colorimetric phosphate procedure; and (5) dissolved solids meter procedure. Background information is also provided. Topics addressed include why water treatment of marine engineering plant water is needed (breakdown of composition of seawater is provided); how water impurities cause deposits; mineral deposits, scale (any solid material found on boiler tubes or inside drums after water has been drained out), and sludge; chemistry of scale and scale prevention; chemical composition of boiler water suspended solids; water corrosion of boiler metal; theory of corrosion, discussing chemical reactions at the anode and cathode; other kinds of damage from corrision; and evaporator water problems. (JN)