Residential building practice currently ignores the losses of energy and water caused by the poor design of hot water systems. These losses include: combustion and standby losses from water heaters, the waste of water (and energy) while waiting for hot water to get to the point of use; the wasted heat as water cools down in the distribution system after a draw; heat losses from recirculation systems and the discarded warmth of waste water as it runs down the drain. Several technologies are available that save energy (and water) by reducing these losses or by passively recovering heat from wastewater streams and other sources. Energy savings from some individual technologies are reported to be as much as 30 percent. Savings calculations of prototype systems including bundles of technologies have been reported above 50 percent. This roundtable session will describe the current practices, summarize the results of past and ongoing studies, discuss ways to think about hot water system efficiency, and point to areas of future study. We will also recommend further steps to reduce unnecessary losses from hot water distribution systems.