A thermostatic shut-off valve, either integrated into a showerhead, or as an add-on positioned between the showerhead and shower arm.  When hot water is called for, the shower flows normally, expelling the cold water “plug” in the plumbing system until hot water is flowing.  At that point, the valve shuts off, and water flow is reduced to a trickle.  The consumer opens the valve when they wish to begin showering.  Once the shower is completed, the valve resets.

The manufacturer claims that their product significantly reduces “behavioral waste” caused by consumers turning on hot water at the shower, and letting it run unused until well after the point that a comfortable showering temperature (95° and upwards) is achieved. A study by Lawrence Berkeley Laboratories suggests that typical behavioral waste events last between 38 and 56 seconds, and represent 1.7 to 4.9 gallons per event (Sherman, 2014).  Assuming an average Seattle cold water temperature of 58.4°F (Seattle average annual air temperature of 52°F (USCD, 2015) plus 6.4°F (Per Philip Fairey, Florida Solar Energy Center, this is a consistently predictable guideline for determining inlet temperatures, and the basis for RESNET’s upcoming water index baseline for water heating energy use.)) this represents between 638 and 1839 Btus of wasted energy per shower.  Using LBNL assumptions of .75 showers per capita per day, and 2.8 persons per household (Lutz, 2005), this represents savings of between 117 and 336 kWh per year.

In addition to energy savings, there is the value of the water saved – 1303 to 3756 gallons per year.  This savings is not only realized by the end user, but by decreased impact on water supply and treatment energy use.

The Regional Technical Forum has performed preliminary analysis on this product, and estimate annual savings of between 30 kWh per year (for a 1.5 gpm showerhead, heated by a heat pump water heater) and 120 kWh per year (for a 2.5 gpm showerhead, heated by electric resistance water heat).  While these numbers are significantly less than the above estimates, the RTF savings estimates assume less than half as many showers per year than the LBNL data.  The RTF has allocated staff resources toward developing a provisional measure for this product (RTF, 2014).  According to the manufacturer, a final determination of deemed savings will be made in July 2015.