Waste Water Heat Transfer Systems, LLC, Stop wasting your existing hot liquid resource by pouring it down the drain. Put it to work by exchanging that energy back into your fresh water supply. Our unique fresh water heat exchanger transfers heat from any hot liquid source to your fresh water supply. Or your need may be to reduce the temperature of the hot waste stream, cooling it in order to dispose of it directly into waste drains. ROI 18 to 30 months.