Reusing Graywater

One such alternative source is graywater, which includes filtered, untreated wastewater from washing machines, showers, bathtubs, and lavatory faucets. This water can be collected using separate drain lines, filtered to remove large particles, such as lint, stored for short periods of time, and distributed to irrigation systems. Because the water is not usually treated enough to remove bacteria, in some jurisdictions whole-building graywater regulations limit applications to below ground irrigation, where human contact is unlikely.

The on-site waste-water treatment plant at the Solaire uses a combination of biological treatment, micro-filtration, and UV treatment to produce safe, nonpotable water. The high-tech system was one of the first of its kind in the U.S. Photo courtesy Solaire (top); illustration by Clifford Rumpf (bottom)

Graywater systems are far from common, but those that exist are most often found in residential and small commercial buildings rather than in large buildings. While most states prohibit graywater recycling, regulations addressing graywater are gradually appearing as more regions deal with drought. Following the drought in the Southeast, for example, the city of Savannah, Georgia, adopted regulations in early 2008 that permit graywater use, but only for toilet flushing and only after chemical treatment.

In addition to whole-building graywater collection, self-contained units such as the Aqus graywater system, from WaterSaver Technologies (also marketed by Sloan Valve Company), collect graywater from a single lavatory sink and use that water for flushing an adjacent toilet.

On-site Wastewater Treatment

In a small number of commercial buildings, all wastewater generated by the building (graywater as well as blackwater, or water from sewage systems) is treated on-site to very high standards and reused for nonpotable applications. The Solaire, a 293-unit high-rise residential building in New York City completed in 2003, incorporates one of the first such systems. A combination of biological treatment (aerobic and anaerobic), hollow-fiber microfiltration, and ultraviolet (UV) treatment purifies more than 25,000 gallons of wastewater per day. Of this treated water, 9,000 gallons are used for toilet flushing throughout the building, 11,500 gallons are used as makeup water for the building's cooling towers, and 6,000 gallons are used for landscape irrigation. This treatment and reuse system was designed and installed by Applied Water Management Group, a subsidiary of American Water, Voorhees, New Jersey.

The Australian company Perpetual Water manufactures a range of graywater systems, including this home system. On the right is a unit in which graywater is treated to Australia's Class A standard. After treatment, the water is stored in the cylindrical tank on the left, then used as needed for irrigation, toilet flushing, or clothes washing. Photo courtesy John Grimes/Perpetual Water

Another type of on-site water treatment system is variously known as ecological wastewater treatment, a Living Machine, or Solar Aquatics. This is a more biological process that mimics the cleansing function of wetlands. It combines plants, bacteria, and other microorganisms in a balanced ecosystem to create wastewater treatment facilities that are functional and beautiful. This technology, developed by biologist John Todd, has been installed in a handful of green buildings around the country, including the Lewis Center for Environmental Studies at Oberlin College, in Ohio, completed in early 2000.

Municipal-Scale Treatment

Far more common than on-site systems are facilities that reclaim water from municipal sewage treatment plants for nonpotable applications. The nation's first utility-scale reclaimed water system, in St. Petersburg, Florida, began operation in 1977. Today, there are 1,600 reclaimed-water systems operating in 25 states, according to the WateReuse Association, Alexandria, Virginia. The St. Petersburg plant, still one of the nation's largest, includes nearly 300 miles of pipe and delivers an average of 21 million gallons of reclaimed water per day.

Pipes that carry reclaimed water (treated waste-water) for nonpotable uses, such as these in Denver, are often painted purple or pink to distinguish them from potable-water pipes. Photo courtesy Denver Water

Reclaimed water is highly treated and provided through a separate piping network from potable water. In North America, reclaimed water is used only for nonpotable applications, most commonly for irrigation. It is also used as makeup water for cooling towers, toilet and urinal flushing, and industrial process needs. Piping for reclaimed water is often painted purple to clearly distinguish it from pipes transporting potable water.

In some areas of California, buildings over a certain size are required to be dual-plumbed for reclaimed water use (referred to as "recycled water" in California). In the Irvine Ranch Water District south of Los Angeles, for example, this requirement applies to all buildings seven stories or taller. California's Title 22 regulations clearly spell out what level of treatment is required for agricultural, urban landscape, and commercial/industrial applications (see table, page 114). Nationally, recommended practices for reclaimed water use are addressed in the U.S. Environmental Protection Agency'sGuidelines for Water Reuse, published in 2004.