A method and apparatus of sanitizing drinking water to be dispensed from a water dispenser having a reservoir includes the steps of providing the ozone gas generator that generates an ozone gas stream, transmitting the ozone gas stream from the generator to the water dispenser reservoir, mechanically breaking up the ozone gas stream inside the reservoir to produce ozone gas bubbles, and using the ozone gas bubbles to disinfect water in the reservoir. The ozone gas stream can be mechanically broken up using a pump such as, for example, an impeller type pump.