Fluid flows through solar collectors on the roof and returns to a large, well insulated solar storage tank to preheat the household water. When hot water is needed in the house, the preheated water flows through the traditional water heater to "finish up."  In summer months, the solar heated water can reach temperatures of 150-160 degrees F, and the traditional water heater does not turn on at all. In winter months, the solar water reaches temperatures of 90-100 degrees F, so just a little input from the traditional water heater is needed.  The fluid pumped through the collectors is a mixture of glycol and filtered/deionized water. The mix will not freeze down to -30 F. Solar water heating can be used with oil, gas or electric traditional water heaters.