The effects of storage tanks on water quality within the tank and in the distribution system may be studied through field sampling programs, physical models of tanks, or through computer modeling of tanks. In several recent studies, field sampling programs have documented the variation of water quality within tanks. Bench level models of water tanks are also being used as a means of studying the movement of water within a tank and the subsequent variation in water quality. The third method of studying water quality in a tank, computer modeling, is the subject of this paper.