Conservation Matters January 2013

The Texas Land, Water and Wildlife Connection

Can graywater keep Texas landscapes green?

Graywater El PasoWith water resources throughout Texas becoming scarcer, a Texas A&M AgriLife Research ornamental horticulturist is working with others to determine the feasibility of using graywater to irrigate home landscapes.

"There has been interest in and discussion about the possible use of graywater for irrigating home landscapes, but so far little formal research has been done to validate its practicality," said Dr. Raul Cabrera, of the Texas A&M AgriLife Research and Extension Center in Uvalde.

Cabrera said graywater is essentially "soapy" water left after tap water has been run through a washing machine or used in a bathtub, bathroom sink or shower and does not contain serious contaminants.

He said while it is difficult to precisely estimate the statewide potential for water savings through the use of graywater and application of the technology needed, it may reduce household landscape water use by up to 50 percent, depending on the size, type of landscape plants used and geographical location.

"The average household uses as much as 50-60 percent of its water consumption for the landscape—grass, ornamental plants, trees, etc.," he said. "Considering that the average family of four produces about 90 gallons of graywater per day, if this was used to irrigate a landscape, it could represent a significant water savings."

Cabrera said this would be especially true for a large city such as nearby San Antonio, which has more than 1.3 million people in its metropolitan area.

"Implementing the use of graywater for landscape irrigation across the state could mean a tremendous water savings in terms of acre-feet of water, contributing to the water use and conservation goals of the recently released 2012 Water Plan," Cabrera said.

Using graywater is one of the easiest ways to reduce the need for potable water typically used in a home landscape, said Dr. Calvin Finch, director of the Water Conservation and Technology Center (WCTC) in San Antonio, which is administered by the Texas Water Resources Institute (TWRI) and Texas Center for Applied Technology (TCAT).

TWRI is part of AgriLife Research, the Texas A&M AgriLife Extension Service and the College of Agriculture and Life Sciences at Texas A&M University. TCAT is part of Texas A&M Engineering Experiment Station. TWRI is participating in the graywater research, as well as providing funding.

Finch said the 2012 state water plan identifies more than 500 specific activities that, if implemented, would help meet the state's future water needs.

"One of the low-hanging fruit projects that is often overlooked is use of graywater from households," he said. "Research results indicate that, with minimum precautions, water from our showers, bathroom sinks and clothes washers could be used to meet up to 10-15 percent of our overall landscape water needs."

Graywater differs from reclaimed water in that it is not captured water from sewer drainage or storm-water systems and then run through a waste-water treatment facility, Cabrera said.

"Reclaimed or 'purple-line' water is used for irrigation by some large-acreage operations such as golf courses, sports fields and large businesses," Cabrera said. "But graywater is just potable water that has been used for fairly benign household activities and could be reused immediately or stored and used soon after its initial use.

"It is also not what is referred to as 'black' water, which is used water from a toilet or the kitchen sink, both of which have a higher potential for containing bacteria and other organisms considered hazardous for human health. In this regard, graywater poses a minimal risk, particularly if we look primarily at water generated from clothes-washing machines."

He said some southwestern U.S. states, including parts of Texas, already allow for the use of graywater under certain restrictions, such as irrigation through delivery by flooding, subsurface or drip irrigation.

"While graywater has little potential for containing hazardous organisms, such as coliform bacteria, these irrigation distribution methods are preferred to spraying in order to further ensure safety," he said.

Cabrera said collaborating entities working to evaluate the viability of graywater use include AgriLife Research, AgriLife Extension, TWRI, WCTC and TCAT.

Read the full AgriLife TODAY article for more information.

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