What is the maximum flow rate allowed for faucets?
In the U.S., the Energy Policy Act of 1992 and subsequent rulings by the U.S. Department of Energy (DOE) set the maximum lavatory faucet flow rate at 2.2-gallons per minute (gpm), or 8.3 Litres per minute (Lpm), when measured at 60 pounds per square inch (psi) of flowing water pressure.
However, the governing standard and test procedure (as established by the DOE) for faucets in the U.S. was and continues to be the ANSI national standard, ASME A112.18.1/CSA B125.1. In the 1990s, this standard was changed to reflect a lower maximum flow rate of 0.5-gpm (1.9-Lpm) for all "public" applications. All of the major U.S. plumbing codes have adopted ASME A112.18.1/CSA B125.1 by reference.
The maximum flow rate in the U.S. for lavatory and kitchen faucets in residential applications is 2.2-gpm (8.3-Lpm). The U.S. EPA's WaterSense program offers an alternative approach to water efficiency by labeling certain high-performing residential lavatory faucets that function at lower flow rates (see below).
Public vs. private applications
"Public" applications are defined in those implementing codes as all applications that are NOT defined as "private". The codes (Uniform Plumbing Code, International Plumbing Code, and the National Standard Plumbing Code) each define "private" as inclusive only of fixtures in residences, hotel/motel guest rooms, and private rooms in hospitals. All other applications are deemed as within the "public" category and subject to a 0.5-gallons per minute maximum for lavatory faucets. This includes such applications as single-tenant and multi-tenant office buildings, schools, gymnasiums, manufacturing facilities, public buildings (including those where the general public is denied access), bars, restaurants, retail stores, and any other type of building that does not fall within the "private" definition.
Metering faucets are subject to the same codes and standards, all of which set the maximum water use at 0.25 gallons per cycle. That is, the "on-off" cycle (or time during which the faucet is on) cannot result in a total flow in excess of 0.25 gallons of water (0.95 litres). Metering faucets are not subject to a maximum flow rate. Hence, if a cycle is 15 seconds, then that means the flow rate can be as high as 1.0 gpm (3.79 Lpm). A 20% reduction may be achieved by shortening the cycle to 12 seconds at 1.0-gpm (3.79 Lpm), leaving sufficient water for washing one's hands.
Recently, the U.S. EPA's WaterSense product labeling program approved a specification for residential lavatory faucets in which the maximum flow rate is set at 1.5-gpm (5.7 Lpm) and the minimum at 0.8-gpm (3.0 Lpm). Some WaterSense faucet links include:
Do sensor-activated commercial faucets actually save water?
In the past several years, the commercial side of faucets has been a topic of much conversation, if not research. Most water efficiency practitioners readily acknowledge that sensor-activated flush valves (for commercial toilet and urinal fixtures) save no water. In fact, they would quickly say that these devices waste water by flushing more frequently than necessary! But, what about faucets?
Several independent studies indicate that sensor-activated faucets save no water at all. In fact, typical sensor faucets have been shown to result in higher water use when compared to manually operated faucets.
Millenium Dome Report on Water Efficiency-"Watercycle" (2002)
Thames Water's "Watercycle" project at the Millennium Dome in London was one of the largest in-building recycling schemes in Europe, designed to supply up to 130,000 gallons per day of reclaimed water for WC and urinal flushing. It catered to over 6 million visitors in the year 2000. Overall, 55% of the water demand at the Dome was met by reclaimed water. The Dome was also the site of one of the most comprehensive studies ever carried out of water conservation in a public environment, evaluating a range of water efficient appliances and researching visitor perceptions of reclaimed water.
Of particular interest is Figure 6 in the Millenium Dome report that shows washroom water use for handwashing and compares infrared sensor-operated faucets with "push top" (cycling) faucets and conventional swivel top faucets. It confirms that infrared sensors on the faucets create a waste of water when compared to conventional fixtures.
ASHRAE Field Study (2002)
Another study that compared manually operated faucets with sensor-activated faucets was published in 2002 by ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.). While not the main focus of the study, titled "Field Test of a Photovoltaic Water Heater", Tables 3 and 4 provide data needed for the comparisons.
Hillsborough Sensor Valve Study (2010)
This study (report attached to my email) focused on all types of sensor-activated valves for the commercial restroom, including faucets, toilets, and urinals. Again comparing manually operated lavatory faucets with sensor-activated faucets, the study found that faucet water use increased by 30 percent when the former were replaced by the latter.
West Basin Sensor Faucet Study (2010)
In a study at a chain hotel in Southern California, manual faucets in four public restrooms were first fitted with 0.5-gpm (1.9-Lpm) aerators and water use measured. Subsequently, the faucets were replaced with sensor-activated products also equipped with the same aerator model. Water use was measured after replacement and was found to have reduced only 0.4 percent in total consumption over the entire 77-day study period.
CONCLUSION: It is NOT the activating sensor that can yield water savings, but rather the aerator on the faucet. In a commercial setting, faucets set to operate at the code and standards maximum of 0.5-gpm (1.9-Lpm) as noted above will see no difference in water use between a manually activated and a sensor-activated faucet.