The relatively low temperature of thermal discharges from steam-electric power plants makes waste-heat utilization difficult without modification of the power cycle and attendant reduction in electrical energy generated. In situ beneficial use of waste heat by direct once-through condenser discharge into a municipal water supply is discussed. Computations are presented regarding the matching of flow rates, heat losses in distribution and energy savings. A number of benefits and penalties are also assessed qualitatively including legal and operational aspects and reliability. Especially attractive are improvements in electrical generating efficiency, and savings in water-heater energy. Secondary advantages include alleviation of pipe freeze up in winter and improved efficiency of slightly heated waste-water treatment. Penalties include additional pumping power for distribution in the water supply due to increased back pressure on the steam turbines which employ condensers cooled by the water they pump. Additional chlorine is also required to maintain a residual concentration in the distribution system. There may also be difficulties with public acceptance of water preheated by up to about 24/sup 0/F, especially in summer. The water supply of greater Chicago and 4880 MW(e) of colocated fossil-fired load-following generating capacity were analyzed as a hypothetical test case. It was concluded that the net annual energy savings is 23 x 10/sup 12/B, equivalent to 4 million bbl of oil, with a net savings in cost of $12./capita for the population of 4.66 m. While not developed for energy conservation purposes, three actual systems with operating experience are summarized. In order to determine feasibility of application, site-specific systems analysis is required.