DOE, EERE, FEMP. Best Management Practice: Alternate Water Sources.
Alliance for Water Efficiency (AWE). Graywater Introduction.
Rainwater collection systems can be practical in all regions of the country, including
those that experience frequent precipitation and more arid regions where water sup-
plies are scarce. The major components of a rainwater collection system include:
Roofs or surfaces where rainwater can be collected
Gutters and downspouts to transport the rainwater to storage
Gutter screens to remove debris
Storage tanks (cisterns)
Conveyance systems to deliver stored water
Water treatment, depending upon end use quality requirements
Rainwater that runs off of non-roof surfaces, such as parking lots, hardscapes, and
landscapes, around a building can also be a good source of water for landscape
irrigation, provided it can be captured, treated, and stored. Generally, this collected
water can be captured and distributed from onsite features, such as berms, swales,
or rain gardens, or can be diverted to a long-term storage detention pond, where
the water can be pumped for landscape irrigation or other uses.
The quality of
rainwater collected from the ground is much more variable than that collected from
rooftops, because it can pick up pollutants as it travels across the landscape. It is
important to carefully consider the water quality needs of the end use or provide
appropriate treatment before rainwater is used.
Gray water is wastewater from lavatory sinks, laundries, and bathing. It never con-
tains wastewater from toilets or urinals and excludes wastewater from kitchen sinks.
Gray water can be treated and reused for specific onsite applications; however,
health and safety concerns must be considered. Treated gray water should always be
used within 24 hours of collection, or otherwise properly disposed, because it can
foster bacteria and pathogens. If treated gray water is used for irrigation, it should
only be applied below the surface and should never be used on plants intended for
human consumption or sprayed through conventional sprinkler heads where it has
the potential to be inhaled.
The use of treated gray water as an onsite alternate water source requires a careful,
site-specific analysis. Gray water is usually coarsely filtered to remove large, sus-
pended solids and, when used for indoor purposes, is usually further sanitized with
chemicals such as chlorine. The lowest level of treatment is typically sufficient for
subsurface irrigation applications. More intensive treatment is necessary for other
applications, including toilet and urinal flushing or above-ground irrigation. If con-
sidering installing a graywater treatment system, consult local health department
officials first to ensure that the system meets appropriate regulations. Also, consult
the manufacturers of the fixtures and equipment to which non-potable water is to be
delivered to determine under what conditions those items can function with treated
gray water and what impact such use will have on fixture and equipment warranties.
Onsite Alternative Water Sources