BackPage Primer from Environmental Building News
March 1, 2009
Graywater Collection and Use
Graywater is wastewater that has been used in clothes washers, showers, bathtubs, and lavatory sinks. In some parts of the country graywater may be collected using separate drainage pipes, then filtered and temporarily stored (without treatment) before being distributed in subsurface outdoor irrigation. There are also systems that direct lavatory washwater to an adjacent toilet tank to be used (after limited treatment with disinfectant) for toilet flushing.
Blackwater describes wastewater from toilets, urinals, kitchen sinks, and dishwashers, which may contain food and human waste and is not as easily reused.
Graywater is typically stored inside a building rather than discharged immediately, because enough volume needs to be available to distribute it evenly through irrigation pipes. A significant amount of organic matter, including fats from soaps, is present in graywater. Aerobic bacteria decompose this organic matter, robbing the water of oxygen. Once the oxygen is depleted, anaerobic bacteria will take over, producing methane and foul-smelling hydrogen sulfide. To prevent this, storage time should be short before the tank is emptied into the subsurface irrigation system.
Graywater systems are worth considering in areas where droughts have resulted in restrictions on potable water use outdoors or in projects where either water use reduction or wastewater reduction is a high priority, such as LEED projects seeking the highest level of certification. Whole-building graywater systems are most practical for buildings that have outside landscape area where subsurface irrigation is feasible.
Whole-building graywater systems are neither simple nor inexpensive, and safety restrictions in building codes can make them particularly complex. In most places, such systems are not permitted at all. Exceptions include Arizona, California, New Mexico, Massachusetts, South Dakota, Texas, Utah, and Savannah, Georgia. Statewide graywater regulations are scheduled to be implemented in Montana, New York, Oregon, and Washington. Even in areas where whole-building graywater is not an option, it might be possible to recycle lavatory wastewater into an adjacent toilet for flushing.
Whole-building systems must have dual drainage piping for wastewater. Graywater collection and storage systems must be prominently marked and completely separate from potable water and other wastewater systems to prevent mixing. Even if graywater is not going to be reused immediately, some designers and builders provide separate drainage plumbing so that a graywater system can later be installed with minimum disturbance and cost.
The costs of graywater systems are highly variable and depend on available expertise and local regulations, which sometimes make graywater systems prohibitively expensive. But as water shortages and drought continue to result in restrictions on outdoor potable water use, graywater will become more popular and costs will drop. Motivations for installing graywater systems will tend to be related to water conservation rather than financial return.
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We received an email from Gabrielle Schiffer with the Oregon Building Codes Division updating us on her state's greywater regulations. Her email reads:
"Oregon’s State Building Codes Division (BCD) approved a ‘statewide’ alternate method (SAM) to the state plumbing code for gray water (we’re calling it water conservation) reuse for flushing toilets in residential and commercial buildings during 2008. You can find copies of the SAMs on gray water reuse on our green building services webpage http://www.cbs.state.or.us/external/bcd/programs/green.html
Secondly, HB 2080 is currently moving through the state legislature. If approved, it will direct the Oregon Environmental Quality Commission to adopt rules for more expanded use of gray water including irrigation.
Right now you can find our newly published ‘smart guides’ on water conservation (both rainwater and gray water) posted on our home page at http://www.bcd.oregon.gov."