Two components of water use in a shower are flow rate and duration. The National Energy Policy Act of 1992 (EPAct 92) mandates that all showerheads manufactured, sold, and/or installed in the U.S. operate at a flow rate that does not exceed 2.5 gpm (9.5 Lpm). Showerheads sold prior to 1994 will usually have higher flow rates; many of these showerheads still exist in homes and apartments.

Prior to 1980, many showerheads exceeded 5 gpm (18.9 Lpm) in flow rate. In the mid-1980s, a number of states restricted flow rates to a maximum of 3.5 gpm (13.2 Lpm), and then later to 3.0 gpm (11.4 Lpm). To eliminate confusion and state-by-state differences, EPAct 92 set the national maximum for showerhead flow rates at 2.5 gpm (9.5 Lpm). In December 2010, U.S. States and local jurisdictions were granted permission to set their own showerhead performance requirements.

While some water efficiency practitioners believed that reducing flow rates of showerheads would cause users to take much longer showers, research completed by MaP (using data from the 1999 and 2016 North American Residential End-Use Studies of Water) indicates reductions in flow rates have only a minor influence on the duration of the average shower experience. The three shower-focused MaP reports are available for free download.