Whether you’re installing plumbing in a home or in commercial building, there are a number of things you can do to make your building more sustainable and green. Plumbing drainage systems, for example, have an enormous impact on the environment.
   Gray water recycling systems are a big part of what we call sustainability construction. A building’s cost can be reduced substantially if a gray-water recycling system is incorporated in the planning stages of the buildings plumbing system.
   Gray water is the waste discharge from those fixtures that do not or are not intended to receive human bodily waste (urine, feces) or food waste, and its supply piping should never be interconnected with any non gray-water piping. Further, water containing human bodily waste is commonly referred to as “black water.” Fixtures that can use gray water for flushing are water closets and urinals because neither requires potable water to function properly.
   Raw gray water to be used in fixtures must be filtered, disinfected and identified by color, effectively reducing the potential health risks and any objectionable odors or appearances. Gray water can also be used for subsurface irrigation of yards, lawns, gardens, plantings, etc, but does not have to be disinfected or dyed when used for this purpose.
   A building designed for gray-water recycling will have two independent fixture drainage collection systems. The non gray-water drainage system will discharge directly to the building sewer and the gray-water drainage system will discharge to a reservoir/treatment system. The venting systems can be independent or combined. The building will have two independent water distribution systems, one for potable water and one for treated gray-water.
   Filtering gray water is an important step in the disinfecting process. Without filtering, the entire system would be contaminated with debris that could cause, among other things, fixture flush valve and fill valve damage, pipe blockages, pump damage, increased maintenance needs, bacterial growth, odors and unsightly plumbing fixtures. Unfiltered gray water would also be more difficult to disinfect effectively. 
   Diatomaceous earth is a siliceous earth composed of the shells of algae plants known as diatoms. It’s commonly used as a filter medium in swimming pools. Disinfection methods will be greatly affected by the efficacy of filtering. To simplify maintenance and avoid a health risk to maintenance personnel, the filtering system should be designed to allow backwashing the filtered debris directly to the sanitary drainage system. Disinfection is not required for subsurface landscape irrigation systems.
   Another important component of the gray-water recycling system is makeup water. In systems for flushing water closets and urinals, potable water must be provided to make up for any shortage of gray water. 
   Depending on the circumstances, the flushing water demand could exceed the production of gray water, and makeup water would be necessary. It is imperative that the potable water supply be protected from contamination. Connecting potable water piping to a gray-water reservoir is an extreme health risk requiring dependable protection against backflow. An air gap would be ideal, but might be difficult to install because the reservoir must be a gas-tight vessel. It might be feasible to install an air gap arrangement where the potable water enters the vessel through an open trapped inlet pipe or a gray-water discharging fixture. 
   Another acceptable method of backflow protection for this situation is the installation of a reduced pressure principle device. Because irrigation is not a demand like a fixture that requires flushing water, a makeup water system isn’t required for a subsurface landscape irrigation system.
   To design a subsurface landscape irrigation system, the rate of absorption of the soil must be known. Protection of ground water sources as well as any water reservoirs is also necessary. The distance from buildings and property lines are also crucial information that plays a roll in the design of a system.
   Gray water recycling is a big component of sustainable construction and will continue to play an important role in a world of limited natural resources. Conservation needs and concerns are growing internationally and will become more desirable and possibly mandated.