The American Society of Heating, Refrigerating and Air-Conditioning Engineers, American Society of Plumbing Engineers, American Water Works Association, and U.S. Green Building Council have jointly issued a draft standard on water efficiency for buildings, mechanical systems and building sites, and are seeking public comment on the document through December 10, 2012.

The draft states that one third or more of water consumption for a typical office building is devoted to heating, ventilation and air conditioning (HVAC) systems. It proposes standards to “balance environmental responsibility, resource efficiency, process efficacy, and community sensitivity,” while supporting development that meets present needs without compromising the ability of future generations to meet their own needs. The standard provides baseline requirements for building designs, sites and mechanical systems to reduce the amount of water needed for HVAC, plumbing and irrigation systems. It would apply to new buildings and renovations that add new portions to existing buildings. The proposal does not apply to storm or building wastewater management or industrial process systems.

The proposal calls for use of diverse landscape plantings and landscape design that reduces supplemental irrigation water use by 40 percent from a baseline calculated using the U.S. Environmental Protection Agency’s water sense budget tool. Dedicated athletic fields are exempt from this requirement. The proposal generally calls for vegetative roofs to either use no irrigation or to irrigate using only alternative water sources once vegetation is established. It calls for use of filtered backwash water from pools and spas for landscaping and other applications. It also calls for mandatory use of municipally reclaimed water for cooling tower make-up water and toilet and urinal flushing when such water is available within 1,000 feet of a property boundary. The draft standard would require that availability of non-potable water sources such as rainwater, drain system and storm water, and gray water be considered, unless either the total potential use or total availability of such water is less than 250 gallons per day.

The draft contains maximum water use limits for a variety of needs, including toilet flushing, faucet flow rate, showerheads and residential appliances. It sets a 32-ounce limit on the volume of water piped between hot-water systems and the fixtures they serve, and requires insulation of pipes carrying hot water. The draft also contains a series of best practices for design and operation of HVAC systems.