Abstract: Domestic water conservation piping system has thermostatically controlled diverter valve in series with water heater and shower head and/or a hot water shunt tube extending from the hot water heater to the fixture hot water supply in parallel with the thermostat piping. When low temperature water is detected in the "hot water" line, the thermostatically controlled diverter valve diverts the low temperature water to a secondary water closet which stores the water at atmospheric pressure. The secondary water closet provides make-up water to a toilet's primary water closet.