Experts investing graywater for 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, associate professor of ornamental horticulture at the Texas A&M AgriLife Research and Extension Center at 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 by using graywater, it may reduce household landscape water use by up to 50 percent, depending on the size and type of landscape plants used and the household’s 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.”
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), both part of the Texas A&M University System. TWRI is participating in the graywater research by providing funding through its Rio Grande Basin Initiative. The initiative is administered through the U.S. Department of Agriculture’s National Institute of Food and Agriculture.
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 water captured from sewer drainage or stormwater systems and then run through a wastewater 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.”
Cabrera said one concern about using graywater 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. “Part of our research here will involve determining the salinity and specific constituents found in graywater and their effect on plants, plus determining the efficacy and function of irrigation systems.”
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.
“Additional research will address how variations in water quality, such as soft versus hard water, may affect the salt content and chemical constitution of the produced graywater and how it affects plant growth and quality,” Cabrera said.