This paper explores the current relationship between low-flow fixtures and energy efficiency standards and incentive programs. In some sectors (notably multi-residential buildings), the energy required to heat service hot water can represent a large portion of building energy consumption. The Ontario Building Code currently mandates maximum water fixture flow rates. There are several commercially available fixtures with flow rates that are below these maximums, however the Ontario Building Code does not currently allow low-flow domestic water fixtures to be considered as a creditable measure when applying the performance path for energy saving compliance. Some green building rating systems, such as LEED, do consider low-flow fixtures to be an efficiency measure, and encourage their use by allowing designers and energy modelers to consider them as a credit in energy calculations. This study addresses the following key questions: How are low-flow fixtures credited under current energy standards or energy efficiency incentive programs? Is there evidence that low flow fixtures actually save water and, if so, by how much? Do energy models appropriately predict annual hot water usage? And finally, what are the appropriate energy savings measure inputs to use in a Savings By Design modelling activity?