After drinking water has been treated with chlorine or chloramine, it will typically flow through storage reservoirs, water tanks, and/or water towers in the distribution system. Water in these reservoirs can become stagnant and develop an unacceptably long water age, leading to a loss of disinfection and/or the formation of nitrites and/or nitrates as well as unpleasant tastes and odors. In order to maintain uniform water age, eliminate stratification, keep water fresh, and reduce treatment costs, solar-powered circulators can be put inside the tanks with their solar modules placed outside on top of the tank. San Francisco and Las Vegas are two cities with high-profile water systems that have adopted this method of keeping their treated water at high quality.