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Potable Water: Every Drop Counts
By David L. Sheridan

David L. Sheridan, PE, PhD, LEED® AP, and principal in Aqua Cura, was educated in civil and environmental engineering, earning a BS at the University of Pittsburgh and an MS and PhD at Penn State University. In 2002, Dave formed Aqua Cura to focus his efforts on critical water issues facing the U.S. Dave served as the first chair of the LEED Water Efficiency Technical Advisory Group, from 2004 to 2008. Dave can be reached at dsheridan@aquacura.com or 717-497-5768.

The Leadership in Energy and Environmental Design (LEED) Green Building Rating System™ developed by the U.S. Green Building Council, encourages potable water efficiency (potable water is water treated to drinking quality) in indoor plumbing fittings and fixtures subject to federal standards: water closets (toilets), urinals, faucets, and shower heads. The Uniform Plumbing Code (UPC) sets a lower flow limit for faucets in public restrooms (see Table 1 for a comparison).
 
LEED Building Design & Construction, the rating system for new construction or substantial renovation, includes a prerequisite that the project achieve potable water efficiency 20 percent better (lower) than the UPC. Points are achieved by measures that improve potable water efficiency as projected by a water use model (see Table 2 for a comparison).

Potable water efficiency can be achieved by decreasing the flush volume or flow rates of fittings and fixtures, or by offsetting potable water with water of lesser quality (for flushing toilets and urinals, for instance). Lower flush volumes can be achieved by opting for high efficiency toilets and urinals. Toilets that use as little as about 1.2 gallons per flush are available. Performance of these high-efficiency toilets can be reviewed on the WaterSense website maintained by the U.S. Environmental Protection Agency (http://www.epa.  gov/WaterSense/). Based on typical toilet use, estimated to be three uses per day by each female building occupant and once per day by each male occupant, annual potable water savings of about 300 gallons per female occupant and 100 gallons per male occupant would be possible with 1.2 gallon per flush toilets.

Potable water use in urinals can be reduced to zero with nowater units or as low as 0.125 (one pint) gallons per flush for some very high-efficiency units. WaterSense has established 0.5 gallons per flush as a threshold for listing and labeling, indicating that this more efficient performance is readily achievable. Based on typical urinal use, estimated to be two uses per day by each male building occupant, annual potable water savings of about 250 gallons per male occupant would be possible with 0.5 gallon per flush urinals. One-pint units would produce annual savings of about 438 gallons, and nowater urinals would produce savings of about 500 gallons per male occupant.

Faucets do not offer significant potential for potable water efficiency. Public restroom faucets are already controlled to 0.5 gallons per minute, a very low flow rate that is adequate for hand washing. Faucets used to deliver a specific volume of water, such as kitchen sinks (filling a coffee pot), should not be constrained to less than UPC requirement.

Showerheads of less than 2.5 gallons per minute should be considered only with great care. Modern shower flow controls incorporate anti-scalding elements that may require a particular flow rate to function correctly. Lower flow showerheads should be chosen only if the flow control is expressly specified to function at the lower flow rate. 

Another strategy to reduce potable water use in toilets and urinals is substitution of nonpotable water for flushing.  Rainwater capture and storage systems can often provide most of the water needed for flushing. The effectiveness of these systems is determined largely by the size of the storage vessel. Rainwater captured from the building roof is relatively clean, and typically requires only filtration and disinfection prior to use for flushing. 

By selecting low-flush and low-flow plumbing fittings and fixtures, and by offsetting potable water for flushing, one can reduce annual potable water use by as much as 1,000 gallons per building occupant.

 
 
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