The Goods on Graywater

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Being a native of the Southwest, and living in Las Vegas for a decade, I've eagerly awaited building codes that support graywater use in our region.  Our water is a precious resource, right?  Recently, our residential clients are beginning to inquire about graywater use as well.

What is Graywater?
According to the California Graywater Code, "Graywater" means untreated wastewater that has not been contaminated by any toilet discharge...and does not present a threat from contamination by unhealthful...wastes.  "Graywater" includes but is not limited to wastewater from bathtubs, showers, bathroom washbasins, clothes washing machines, and laundry tubs, but does not include wastewater from kitchen sinks or dishwashers.

How is Graywater used? 
Graywater is acceptable for use in landscape irrigation, however the landscape system must be designed to prevent ponding or spray of graywater.  If spray irrigation is part of the landscape design, for example at a turf area, then that system must be plumbed separately.  Indoor use is limited to flushing toilets and urinals, and requires an at-site treatment system and tank.  Use of graywater whether new-build or retrofitting an existing home can require parallel plumbing systems in order to segregate plumbing fixtures.  In other words, kitchen fixtures and appliances must be plumbed apart from other acceptable graywater source fixtures. 

Why is the separation of plumbing and uses required? Blackwater, or fecal-contaminated, waste water is obviously something you don't want watering your landscape.  Less obvious is the fact that Graywater can contain pharmaceuticals, salts or other trace contaminants, and even bacteria can be introduced at many points along the system.  While use for an underground drip irrigation system is reasonable, caution should be exercised to avoid exposure of humans or animals to chemicals or pathogens.

Building codes are developed for a broad population and take into account a spectrum of behaviors that can include playing in sprinklers, pets drinking from toilets, adding a vegetable garden to a back yard, disposing of medications or rinsing a cloth diaper in a sink.

What is the current state of graywater in Southern Nevada? 
Currently, a graywater application would be evaluated on a case-by-case basis. This creates a lot of challenge and expense for early adopters.  An example of a project using reclaimed water is the Springs Preserve. 










Legislation to allow graywater and rainwater use is pending in California, in part as an outcome of Vision2020.  In 1991, San Francisco passed a county and city ordinance  requiring that buildings plumb for reclaimed water. This is a redundant system of purple pipes that allows for the use of reclaimed water once a source is available.  Now, the Eastside Recycled Water Project is preparing to deliver recycled water to tap by 2020.  The local utility, San Francisco Water Power Sewer also promotes the following programs, and hosts a design manual:
To pioneer the use of graywater in the City, we offer a Laundry-to-Landscape Graywater Program, a Residential Graywater Permit Rebate, and a Graywater Design Manual for Outdoor Irrigation. We also continue research on the effective and safe uses of graywater and other alternate water sources for on-site reuse in San Francisco.

It’s a fair argument to suggest that all new construction should be using this approach.  Just look around at the many drought notices throughout the United States. It’s likely that reclaimed water will be essential as a resource in this decade.  Some examples of the process of state code adoption include the following:



Typical graywater system features: 
  • Segregation of fixtures 
  • Requirements vary per single-fixture, simple, or complex systems 
  • Signage to distinguish graywater from potable water 
  • Evaluation of groundwater levels and soil absorption, including nearby water bodies 
  • Prohibition of graywater use for spray irrigation 
  • Prohibition of graywater for irrigating edible plants 
  • Requirement of special irrigation emitters and valves to rotate use between zones 
  • Indoor use limited to flushing toilets and urinals (at-site treatment system/tank required)
More resources:

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