Abstract: A vending or dispensing system for providing purified water in response to a customer request is described. The water dispensing system has a water reservoir or tank containing first stage purified water and is provided with a subsystem for circulating water from the reservoir through a microbial sterilizer on at least a periodic basis for a predetermined period of time to maintain water quality within the tank. In one aspect, the water is passed through the microbial sterilizer before entering the tank for the first time as first stage water. Additional features described to insure water purity include flushing or rinsing the lines between a first stage water purification mechanism and the water reservoir prior to topping off the reservoir with purified water, and providing control mechanisms for ensuring that sump liquid cannot be suctioned back into the system.