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Gray Water: The New Green

by Doug Pushard

Gray water has been around for decades. It is the recycling and reuse of waste-water from the shower, tub, clothes washer, bathroom sinks, floor drains for onsite use. This volume of water can sometimes be up to 50 percent of the water consumed inside a typical house. Gray water can easily amount to over 20,000 gallons a month!

Gray water or greywater or grey water are all the same; although, we can’t agree on what we call it, both the plumbing code organizations - the International Plumbing Code (IPC) and the Uniform Plumbing Code (UPC) now have code sections dedicated to detailing how these systems should be implemented.

These new codes have enabled states and local juisdictions to adopt regulations allowing gray water systems to be built. Prior to these codes some states lead (i.e. Arizona and New Mexico) in this area by adopting state-wide codes to allow these systems at a residential level (i.e. the discharge of less than 250 gallons per day). Some states struggled with the concept of allowing gray water systems (e.g. Texas and Colorado), permitting it in some jurisdictions and not others or allowing it but making it very difficult to get a permit (e.g. California); while others still lag in this area altogether (e.g. Utah).

While city water is a great source fo drinking water, it should be secondary when it comes to landscape water use. Below is a summary of the characteristics of each, comparing city drinking water with gray water.

  City Water Gray Water
Drinking Water Quality
Nutrient Rich Low
Chlorine Yes
Very, very low
pH 6.5-8.5 5.0-10.5

Gray water is a great source of irrigation water, which in many locations in the Southwest is 40-50 percent of the overall water use in a home. Gray water usually contains sodium, calcium, magnesium, nitrogen, potassium and other salt compounds. It will also have varying amounts of household chemicals, oils, makeup greases, nutrients and chemicals that can largely be managed by the types of products used wihtin a household.

Chlorine keeps the bacteria in check to ensure the water is drinking water quality. Without the chlorine bacteria will begin to thrive. Bacteria although harmful to humans is helpful for plants. It is the reason untreated gray water systems should be distributed to plants sub-surface.

Many of the nutrients in gray water are exactly the same as the fertilizers we buy at a local landscape store to fertilizer our landscapes. By recycling gray water, you can reduce or eliminate the need to buy expensive plant fertilizers.

The use of the gray water can immediately reduce onsite potable water use during the irrigation season. This saves the household money on its water bill, reduces the energy required to produce the potable water that would have been used on the landscape, and saves energy required at the treatment plant to process this water to teritiary water standards for downstream use.

In New Mexico and Arizona, installing a greywater system does not require a permit for private residential greywater systems that discharge less than 250 gallons per day for use onsite for gardening, composting or landscaping irrigation. There are a few restrictions with the really key ones being: gray water can not be stored for more than 24 hours prior to use; it can not be used in above ground spray irrigation systems; and the water should not contain hazardous chemicals derived from activities such as cleaning car parts, washing greasy or oily rags or disposing of waste solutions from home photo labs or other home occupational activities.

In New Mexico, the development of CloudCroft requires the installation of greywater systems in any new home. In Tuscon, Arizona the City requires the installation of the required indoor plumbing for a gray water system to be installed at the time of construction.

The City of Santa Fe, will soon begin offering rebates for the installation of Laundry to Landscape gray water systems.

Additionally, some of the leaders of gray water resuse are publishing great reference guides:

Now there is even a model ordinance document for jurisdictions to use. This document was written by The Decentralized Water Policy Council and is modeled after the leaders: Arizona and New Mexico regulations.

Gray Water Model Ordinance (pdf)

The QWEL organization out of Santa Monica, CA is providing training materials for local jurisdictions to use. These materials must be modified for local codes but are a good way for water agencies to start the local learning process.

The above guides, model ordinance, and teaching materials will hopefully help others follow.

Living within our water budget is key to a sustainable water long-term future in the southwest. We all depend upon the same primary water sources: Rio Grande and the Colorado Rivers. Reusing our water onsite is not only just makes sense, it helps us stay within our budget. Water reuse is not just for water utilities it is a solution for us all!





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