Abstract: A method of treating domestic, commercial or industrial waste water which includes the steps of mixing the waste water with a coagulant aid so as to bring the pH of the mixture to within a range of about 9.0-10.5, and thereafter adding precipitating agents in at least two successive steps so as to lower the pH of the mixture by about one unit for each step and thereby precipitate solids therefrom until the mixture is approximately neutral. After the addition of each precipitating agent, the precipitated solids are separated from the waste water effluent before the next succeeding precipitating agent is added. Preferably two such successive precipitation steps are performed, after which the resultant waste water effluent is treated with an oxidizing and disinfecting agent, filtered, and then treated with a further oxidizing and disinfecting agent to minimize the B.O.D. level.