AEC Solutions / LEED / Water Conservation

Hand Washing Behavior and LEED

Is it time to amend LEED’s Water Use Guideline?

February 4, 2013

As consumers, we wash our hands many times throughout the day without giving a second thought to the kind of faucet used. However, as professionals specifying commercial faucets we want to be sure we are choosing products that make responsible use of water. The USGBC’s LEED Reference manual and subsequent “Water Use Reduction Additional Guidance” offers strategies for achieving points in Water Efficiency Credit 3 and is often used to guide our decision-making. Therefore, it is important that the thinking underlying the credit is properly aligned with the realities of the various types of commercial faucet technologies.

Unfortunately, there’s a rather significant disconnect with respect to metering faucets and the goal of the credit. Specifically, a misunderstanding of the basic hand washing procedure has resulted in the “Water Use Reduction Additional Guidance” related to USGBC’s LEED Water Efficiency Credit 3 unjustly penalizing some classes of metering faucets available today. To remedy this, we must look closely at hand washing and the differences between the types of metering faucets in order to offer a recommendation for amending this guideline.


Hand Washing Behavior and Water Consumption


Health codes mandate that many classes of service employees adopt the following hand washing procedures:

  • Wet hands
  • Apply soap to hands
  • Lather or work soap into hands
  • Rinse soap off hands
  • Dry hands

Reviewing this procedure closely, only steps 1 and 4 require running water, which prompts two questions:

  • How long does it take to wet hands properly prior to soaping?
  • How much time is needed to rinse the hands completely after lathering?

The total number of seconds needed to wet and rinse hands is the real time value that should be used to determine the volume of water consumed when regulating metering faucets. Instead, the “Water Use Reduction Additional Guidance” regarding Water Efficiency Credit 3 states: “When using a metering or sensor faucet, a default 12-second duration of flow representing the total of all run times during the hand washing process should be used, regardless of the faucet’s cycle time, which might be repeated during the process.”

As is evident from this statement, the current credit treats all metering faucets equally, regardless of design or technology. In fact, there are rather significant differences in the broad category of metering faucets that should affect how they are evaluated in WE Credit 3.


Types of Metering Faucets: Mechanical, Sensor-Activated and Smart Sensor

Mechanical Metering Faucets

Mechanically operated metering faucets have a fixed cycle time. Pushing or twisting a handle accomplishes activation. Once activated, this type of faucet releases water for its entire predetermined duration (known as cycle time) whether or not the water is being used. Only a design change can alter the water volume they use per activation.

A faucet spout’s insert provides aerated, laminated or multiple stream flows, and it determines flow rate as gallons/minute (gpm). The maximum flow rate for manual non-metering commercial faucets—allowed by codes and EPAct ‘92—is 0.5 gpm. Depending on the spray pattern’s quality, this is an adequate minimum for most people.

Sensor-Activated Metering Faucets

Faucets activated by an electronic sensor have a variety of designs differentiated by the type of sensor and its field of sensitivity. These faucets may detect motion, reflective surfaces, heat or interruptions of light. Sensitivity fields (often described as cones of detection) emanate from the sensor’s eye and vary considerably among models. The eye may be located on the wall behind the faucet, on its neck or at the end of the spout.

Sensor faucets have a wide variety of internal intelligence systems, determined by their circuitry design or microchip, which control variables such as the range length, sensor power consumption and frequency of infrared light pulses. In general, smart faucets perform at the level of their circuitry’s intelligence.

Both mechanical and sensor-activated faucets use predetermined cycles of 10 to 60 seconds and release water for the full cycle, whether or not it is being used. Their water-wasting cycle-calibration makes them poor candidates to be allowed under Water Efficiency Credit 3, given its stated objective of reducing water consumption in LEED-certified buildings.

Smart Sensor-Activated Metering Faucets

Smart sensor faucets minimize their water consumption by releasing flow only when hands are present in the water’s path—stopping immediately when they are removed. Therefore, water does not flow unless needed.

To protect them from abuse and to increase water savings, smart faucets shut the water off after a specific number of seconds if the object being detected remains static. This strategy protects them from vandals who try to fool the faucet into running continuously by placing a rag or paper towel in the sink to trigger detection. Unfortunately, this number of seconds has also been referred to as cycle time.


Current Regulations

In 1992, the Energy Policy Act established metering faucets’ baseline water consumption as one of its water use maximums. A faucet’s volume is controlled by time (or flow duration) and flow rate, measured as gallons per cycle (gpc). A cycle equals the number of seconds a faucet allows water to flow once activated.

However, cycle time as defined by the EPAct of ‘92 referred only to mechanical metering faucets. All sensor faucets can be restarted many times without touching their controls. Thus, actual water volume consumed in this process is calculated as:


Volume = (Flow rate) x (total duration of periods of flow)


Smart sensor metering faucets, which are designed to stop water from flowing while hands are not in the water path, should have their usage measured as gallons per cycle where cycle means total flow time. Their flow rate is not required to be as low as 0.5 gpm.

Because a slightly higher flow rate may reduce the time needed to perform steps 2 and 4 of hand washing, it may actually lower the total water volume consumed by reducing rinsing time.


LEED Water Efficiency Credit

The objective of Water Efficiency Credit 3 is to reduce the volume of water use. However, a statement in the aforementioned “Water Use Reduction Additional Guidance” (2009; updated 2012) has been often misunderstood: “The gallons per cycle value must be determined through a separate conversion calculation and then entered into the table. The flow rate is determined using the flow rate in gallons per minute (gpm) and the duration setting (in seconds) for the metering faucet. The default design case duration for auto-control lavatory faucets and metering faucets is 12 seconds. Durations less than 12 seconds are not recommended, as shorter intervals are insufficient for typical hand washing.”

After recent discussions between USGBC staff and its Water Efficiency Technical Advisory Group (WE TAG), this paragraph was revised; it now reads: “The gallons per cycle value must be determined through a separate conversion calculation and then entered into the table. The flow rate is determined using the flow rate in gallons per minute (gpm) and the duration setting (in seconds) for the metering faucet. When using metering or sensor faucet, a default 12-second duration of flow representing the total of all run times during the hand washing process should be used, regardless of the faucet’s cycle time, which might be repeated during the process.”

While this revision alleviated some of the confusion about cycle time, it perpetrates a misunderstanding of proper hand washing procedures, providing no basis in fact for the seemingly arbitrary “default 12-second duration of flow.” Moreover, the continued reference to a need for a conversion calculation from gallons per cycle to gallons per minute departs from the USGBC’s objective by substituting flow rate for volume.


Volume = (Flow rate) x (duration of flow)


A Call for Amendment

Design teams working on LEED-registered projects need to be reassured that they can achieve the reduction in water use required by Water Efficiency Credit 3 when they specify smart sensor metering faucets, which only allow water to flow when hands are in its path. We need to call upon USGBC to clearly distinguish between the types of faucets in use today and clarify their guidelines, which designers are interpreting as regulations. This remedy is long overdue.


 Watch the difference when using a smart sensor faucet to wash hands. 

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