Can gray or ‘soapy’ water keep Texas landscapes green?
By Paul Schattenberg
UVALDE -- With water resources throughout Texas becoming scarcer, a Texas A&M AgriLife Research ornamental horticulturist is working with others to determine the feasibility of using gray water to irrigate home landscapes.
“There has been interest in and discussion about the possible use of gray water for irrigating home landscapes, but so far little formal research has been done to validate its practicality,” said Dr. Raul Cabrera, Texas A&M AgriLife Extension and Research Center in Uvalde.
Cabrera said gray water 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 gray water 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 gray water 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.
Using gray water 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 in San Antonio, which is administered by the Texas Water Resources Institute, part of the Texas A&M University System. The institute is participating in the gray water research, as well as providing funding.
Finch said the Texas 2012 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 gray water 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.”
Gray water 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 gray water 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, gray water 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 gray water under certain restrictions, such as irrigation through delivery by flooding, subsurface, or drip irrigation.
“While gray water 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 gray water use include AgriLife Research, the Texas A&M AgriLife Extension Service, Texas Water Resources Institute, Water Conservation and Technology Center, and Texas Center for Applied Technology.
Cabrera said one concern about using gray water on home landscapes is possible salt content.
“Some detergents may have a high salt content in the form of sodium, chloride, or boron, which could potentially ‘burn’ a plant,” he said.
He said there is also the concern that some of the constituents in soapy water might plug drip irrigation systems, thus requiring additional and periodic care and maintenance.
He said the Texas Center for Applied Technology, part of Texas A&M Engineering, would “evaluate the plumbing and delivery technology needed to retrofit a household” so gray water could be used to irrigate a home landscape.
He added if essential aspects of the initial research are positive, additional involvement might include microbiologists and health officials, to address any perceived health issues or concerns.
Initial gray water testing and evaluation will take from nine months to a year, he noted.
“We hope the results will support the launching and development of a statewide initiative to conserve water resources that will involve many additional partners,” Cabrera said.
Paul Schattenberg is a communications specialist with the Texas AgriLife Extension Service.