Abstract: A heat exchanger placed underneath an elevated tub or shower stall or under the bathroom floor includes a flat top heat conductive plate. The top plate is fastened to a flat lower plate, having a serpentine pattern with a shallow depth embedded into the top surface. When the top plate is fastened and sealed to the lower plate, the flow of the incoming cold water is contained within the confines of the serpentine lower plate of the heat exchanger. Heat is transferred from the grey waste water falling onto the top plate to preheat the incoming cold water flowing underneath the top plate in the serpentine conduit chamber of the lower plate in contact with a bottom surface of the top plate. The cold water is thereby preheated and used as a substitute for the incoming cold water that would be normally plumbed to the discharge shower head.

Abstract: A heat exchanger placed underneath an elevated tub or shower stall or under the bathroom floor includes a flat top heat conductive plate. The top plate is fastened to a flat lower plate, having a serpentine pattern with a shallow depth embedded into the top surface. When the top plate is fastened and sealed to the lower plate, the flow of the incoming cold water is contained within the confines of the serpentine lower plate of the heat exchanger. Heat is transferred from the grey waste water falling onto the top plate to preheat the incoming cold water flowing underneath the top plate in the serpentine conduit chamber of the lower plate in contact with a bottom surface of the top plate. The cold water is thereby preheated and used as a substitute for the incoming cold water that would be normally plumbed to the discharge shower head.