Graywater Use in Green and Sustainable Building
The March 1, 2009 issue of Environmental Building News gives an excellent primer on the topic of graywater collection and re-use in the green and sustainable building effort. I am providing a summary of this timely article here, as it is often a consideration in LEED projects to get credit for the WE Credit 2 -- Innovative Wastewater Technologies. It is also of value in area with water restrictions in areas that experience frequent or chronic drought conditions.
Graywater (sometimes spelled graywater) is water that originates from lavatories, showers, bathtubs and clothes washers. It is NOT water from a kitchen sink or dishwashers, and DEFINITELY NOT from toilets or urinals. In fact, any water that may contain food or human waste cannot be applied here.
Graywater is usually stored on-site in the building and can be used for such applications as outdoor irrigation, and toilet and urinal flushing. It is NOT an easy or cheap item to incorporate into a building design; in fact, many states do NOT even allow it to be used. New York State, and several other states are in the process of creating a state-wide regulation for its use. The states that do allow it are located in the in the arid Western states, such as California, Arizona, Texas, New Mexico, Utah and South Dakota. In the Eastern USA, Massachusetts allows for graywater to be used. To install a graywater system, a two-pipe system of drains must be installed, increasing the complexity and up-front building costs. The system must be clearly marked to avoid cross-connection contamination.
The storage time must be short, as aerobic bacteria will break down the organic matter present in the graywater that originates from soaps, bathing, etc. This will remove the oxygen from the water, giving rise to anaerobic bacterial growth that will now produce methane gas and a VERY foul-smelling hydrogen sulfide. To this end, even graywater that is collected for toilet and urinal flushing will benefit from some limited form of disinfection.
Even where graywater use is prohibited, it may be possible to collect it for immediate adjacent toilet flushing. In any event, many building designers are considering installing the dual piping system during construction, so that if current codes are changed to allow for its use, they are now ready. To install a dual-piped graywater system in an existing building is cost-prohibitive, and would require massive wasteful renovations, further expanding the carbon foot-print.
In general, the motivation for the use of graywater will come from the need for water conservation, not cost savings. As mentioned above, drought-prone areas are the best candidates for this application. In this case, a whole building system will make the most sense, as it can be connected to a water-efficient sub-surface outdoor irrigation system, to meet the limited need for supplemental landscape irrigation in these areas where water-use restrictions do not allow potable water to be used for irrigation. It must be remembered that projects seeking the highest levels of LEED certification will often designing an outdoor landscape that requires NO additional irrigation by the use of indigenous plantings, but graywater use plays a major role here, in that it meets the LEED requirement of up to a 100 percent reduction in the use of potable water. As we know, LEED would really prefer that NO additional irrigation be used. Of course, inside the building, graywater use may be of some help in meeting the WE credits 3.1 and 3.2 -- a 20 to 30 percent reduction in water use, as toilet flushing can accomplished here by the use of graywater.
Graywater (sometimes spelled graywater) is water that originates from lavatories, showers, bathtubs and clothes washers. It is NOT water from a kitchen sink or dishwashers, and DEFINITELY NOT from toilets or urinals. In fact, any water that may contain food or human waste cannot be applied here.
Graywater is usually stored on-site in the building and can be used for such applications as outdoor irrigation, and toilet and urinal flushing. It is NOT an easy or cheap item to incorporate into a building design; in fact, many states do NOT even allow it to be used. New York State, and several other states are in the process of creating a state-wide regulation for its use. The states that do allow it are located in the in the arid Western states, such as California, Arizona, Texas, New Mexico, Utah and South Dakota. In the Eastern USA, Massachusetts allows for graywater to be used. To install a graywater system, a two-pipe system of drains must be installed, increasing the complexity and up-front building costs. The system must be clearly marked to avoid cross-connection contamination.
The storage time must be short, as aerobic bacteria will break down the organic matter present in the graywater that originates from soaps, bathing, etc. This will remove the oxygen from the water, giving rise to anaerobic bacterial growth that will now produce methane gas and a VERY foul-smelling hydrogen sulfide. To this end, even graywater that is collected for toilet and urinal flushing will benefit from some limited form of disinfection.
Even where graywater use is prohibited, it may be possible to collect it for immediate adjacent toilet flushing. In any event, many building designers are considering installing the dual piping system during construction, so that if current codes are changed to allow for its use, they are now ready. To install a dual-piped graywater system in an existing building is cost-prohibitive, and would require massive wasteful renovations, further expanding the carbon foot-print.
In general, the motivation for the use of graywater will come from the need for water conservation, not cost savings. As mentioned above, drought-prone areas are the best candidates for this application. In this case, a whole building system will make the most sense, as it can be connected to a water-efficient sub-surface outdoor irrigation system, to meet the limited need for supplemental landscape irrigation in these areas where water-use restrictions do not allow potable water to be used for irrigation. It must be remembered that projects seeking the highest levels of LEED certification will often designing an outdoor landscape that requires NO additional irrigation by the use of indigenous plantings, but graywater use plays a major role here, in that it meets the LEED requirement of up to a 100 percent reduction in the use of potable water. As we know, LEED would really prefer that NO additional irrigation be used. Of course, inside the building, graywater use may be of some help in meeting the WE credits 3.1 and 3.2 -- a 20 to 30 percent reduction in water use, as toilet flushing can accomplished here by the use of graywater.
Posted by Alan L. Englander at 3/7/2009 1:17 AM 
Categories: Code Restrictions, Plumbing, LEED Credits, Bacterial Growth and Disinfection, Graywater
Categories: Code Restrictions, Plumbing, LEED Credits, Bacterial Growth and Disinfection, Graywater
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