Abstract: A water discharge conduit is disposed in a downwardly inclined direction for receiving a flow of waste water at an upper end, for example, from baths, showers and the like. A water trap is disposed below the conduit in parallel relation and has an intake union to receive a flow of hot waste water from the discharge conduit and a discharge union at an opposite end for discharging the waste water back into the conduit. A plurality of pipes extends through the horizontally disposed water trap for conducting fresh water therethrough in heat exchange relation with the flow of hot waste water in the water trap.