Thermal stratification and fluid motion in solar water storage tanks have been investigated theoretically and experimentally. Transparent glass test sections were used in the experiment to permit visual observation of the flow fields. An electric water heater was used to simulate solar collectors. Experiments were conducted under different conditions in which a solar system is likely to operate. Altogether, about 130 test runs were conducted at various temperatures and flow rates of water at the inlet to the store. It was found that the location of the inlet/outlet ports has considerable effect on the mixing of incoming fluids with those in store