Gray Water as a Resource in Arizona: Prospects and Challenges

Back to Fall 2012 Newsletter

by Chuck Graf, Arizona Department of Environmental Quality

Reusing bath and washing machine water outdoors on plants has become a popular way to save water since California droughts introduced the concept of “showers for flowers”. In 2001, when the Arizona Department of Environmental Quality transformed its gray water rules, such household gray water use was the focus of its effort. Until then, householders desiring to use gray water to irrigate turf and plants had to pay a fee and obtain a written permit from ADEQ. By 2001, after more than a decade of using that “hard-permitting” approach, ADEQ had issued only two such permits.

Yet, an extensive 1999 survey of the greater Tucson area by the Water Conservation Alliance of Southern Arizona, or WaterCASA, and the WRRC found 13 percent of the residences surveyed made some use of gray water. More than half of those systems simply conveyed gray water by hose or pipe from a clothes washer to landscape plants. Still, the results of the survey, when extrapolated to the entire state, meant that about 200,000-300,000 home gray water systems in Arizona were operating without benefit of permit— in other words, illegally.

ADEQ adopted a new approach in 2001, allowing a householder to operate a gray water system if a dozen common-sense best management practices are followed. No registration or application is required. As long as the householder follows the best management practices, the gray water system is considered to comply with a general permit that is written in rule.

Under this new “soft-permitting” approach, ADEQ relies on education and outreach rather than burdensome application requirements and resource-draining permit-writing and enforcement activities. Following Arizona’s lead, other states have since adopted similar approaches to gray water regulation.

ADEQ also developed in 2001 a general permit for larger-scale, non-household use of gray water, but there was little interest at the time. In recent years, interest has grown. Eight large-scale systems have been permitted. The systems range in complexity from a simple shallow, gravel-filled trench at an educational center, used to supply water for landscape irrigation, to a sophisticated 225,000 gallon per day system at a prison that stores, treats, and recycles water from showers for toilet flushing.

Governor Brewer’s Blue Ribbon Panel on Water Sustainability in 2010 highlighted gray water reuse as one component in achieving water sustainability. This prompts the question, how big a role can gray water play?

The City of Tucson has compiled detailed data on water distribution and use that can be used to calculate the amount of gray water potentially available from single-family residences. Tucson estimated the percentages of delivered water used outside, for toilets, washing machines, faucets, showers, leaks, and other. Per capita usage of potable water at these residences in 2011 was 95 gallons per day.

By law, gray water is defined in Arizona as “wastewater that has been collected separately from a sewage flow and that originates from a clothes washer or a bathroom tub, shower or sink but that does not include wastewater from a kitchen sink, dishwater or toilet.” Wastewater from kitchen sinks, dishwashers, and toilets is excluded because of potential health risks associated with the number of bacteria in the water from those sources.

Assuming that one-half of the faucet water is from the kitchen sink, and therefore not gray water, Tucson’s data indicate that gray water could account for 27 percent of total water usage. For a family of four, more than 100 gallons of potential gray water is generated per day. If this volume is substituted for part of the water used outdoors, household water usage would drop by 21 gallons per capita per day—a significant savings. Tucson also compiled data for multi-family residential use. These data indicate that about 30 percent of the supplied water is available for use as gray water if appropriate plumbing is in place. For non-residential sites, the volume of available gray water is harder to estimate. However, potential opportunities for largerscale systems include hotels, office buildings and other workplaces, schools, prisons, car dealerships, car washes, and campgrounds.

While it is clear that a household can realize water savings from gray water reuse, this is not likely to translate into significant water conservation gains in existing residential neighborhoods. There, the difficulty and high cost of retrofitting are likely to create too large an obstacle to extensive gray water use. Appreciable water conservation gains might be achieved in new subdivisions plumbed to separately collect gray water.

On the other hand, more extensive use of gray water may have negative consequences due to reduced sewer flows. The Pima County Regional Wastewater Reclamation Department identified possible impacts that include more sewer line blockages, increased odors, and decreased asset life due to corrosion. Increased operations and maintenance costs, and eventually, capital spending for replacement can be expected. Also, since reduced flows would be most pronounced in the upstream ends of the collection system, sewer lines in these areas will need steeper slopes, which would increase the number of lift stations needed.

Ultimately, a community will have to consider the positives and negatives of implementing gray water policies. For example, on a lifecycle basis, is increased gray water utilization better from the standpoints of water savings, water quality, and cost than centralized or decentralized wastewater treatment and reuse of reclaimed water?

On a positive note, concerns about long-term irrigation of landscape plants by gray water appear to have been answered by a recent study by the Water Environment Research Foundation. Except for a few sensitive plants (lemon tree, Hass avocado, and Scotch pine, for example), the study found no significant adverse impacts.

With more facilities seeking LEED green building certification, which gives points of credit for gray water reuse, ADEQ expects to see continued interest in larger-scale projects and non-household reuse of gray water. However, current permitting mechanisms for such systems are unwieldy and inefficient. The Blue Ribbon Panel recommended that ADEQ streamline permitting provisions for larger systems, including development of general permits aimed at the type of systems under consideration today. The current fee structure for permit applications and renewals also has been criticized as being a disincentive for large-scale gray water recycling.

In any case, while we in Arizona can take pride in being a leader in gray water regulation, there is still more to do to advance the program.