Researchers use gray water use for home irrigation
Inside a greenhouse on the grounds of the Texas A&M AgriLife Research and Extension Service Center in Uvalde, Texas, Raul Cabrera recently inspected several groups of ornamental plants for signs of damage or distress.
“This is the first component of our practical gray-water investigation,” said Cabrera, who along with colleagues from the Uvalde center and the Texas Center for Applied Technology started research in late 2012 to confirm the potential use of gray water for home landscape irrigation.
Gray water, Cabrera said, is basically the soapy water that remains 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.
“We wanted to find out whether or not using gray water to irrigate home landscapes would be a practical thing to do based on its effects on various ornamental plants,” he said. “So we set up an experiment to irrigate various ornamental plants using different types of gray water.”
To perform his research, Cabrera set up sections within the greenhouse where he placed multiple pots or containers of about a dozen different ornamental plants—ranging from herbaceous and flowering plants such as Mexican heather, Asiatic jasmine, lantana and dianthus, to hardy native and adaptive ornamentals such as yucca, agave, oleander and yaupon holly. The plants are irrigated through a network of PVC and plastic tubing from 55-gallon plastic containers that water different sets of each plant species with tap water and three varying degrees of gray water.
“You don’t usually see a washing machine in a greenhouse, but we had one installed so we could run loads with detergent alone, then loads with detergent and fabric softener, then a load with bleach,” he said. “This way, we could produce and use different types of gray water and see how it might affect the growth and aesthetics of different ornamentals, particularly since there would be different chemicals in the water, depending on the detergents and cleaning agents used.”
Cabrera chose what he considered the most popular domestic brands of detergent, fabric softener and bleach for his experiment, using each according to its manufacturer’s recommendations.
After 2 1/2 months of irrigating these various ornamentals with different types of gray water, Cabrera said initial results based on visual inspection of the plants are promising, with a few exceptions.
“As we expected, some of the plants irrigated with the gray water containing bleach in the recommended amounts for laundry showed signs of yellowing and reduced flowering,” he said. “We noticed this particularly in some of the flowering plants we chose, including the lantana and dianthus. We have measured concentrations of chlorine in this gray water that appear to be high enough to create a negative impact on these particular species. We are also evaluating the concentrations of other chemical constituents in gray water that could be harmful for plant growth, like sodium and boron.”
However, Cabrera added, the gray water containing bleach had little effect on the remainder of the ornamentals used in the experiment, particularly the hardier plants like holly, yucca and agave.
“There also was no significant negative impact on any of the ornamentals from the gray water with detergent or detergent and fabric softener combination,” he said. “So far, it looks like these types of gray water hold the best promise for short- and long-term use in irrigation, with the gray water and bleach component mainly having use for longer-lived perennial and woody plants.”
Cabrera said this research is particularly relevant for drought-prone Texas as it may reduce household landscape water use by as much as 10-25 percent or more, depending on the size, geographical location and plant selection. He noted that the average household currently uses about 50 percent of its water consumption for landscaping—irrigating turfgrass, ornamentals and trees.
He added that implementing the use of gray water for landscape irrigation across the state could mean a tremendous water savings in terms of acre-feet of water, contributing to the statewide water use and conservation goals of the 2012 Water Plan.
“Gray water has tremendous potential for water savings, especially in an urban environment,” he said. “Its use is already allowed with some restrictions as outlined by applicable ordinances in some Southwest states. It is also used in parts of Texas, particularly in rural areas. However, most of the information on gray water use for irrigation is anecdotal and to date there has been little actual scientific research on its effects on landscape plants.”
Cabrera said he will continue this first phase of irrigation trials in the greenhouse for another two months as preparations are made for the second component of gray water experimentation.
“The second phase involves establishing an outdoor landscape here at the center,” he said. “For that, we are planting trees and shrubs along with flowering and bedding plants. In this study, we will examine the medium- and long-term effects of gray water on these materials over a two-year period. Furthermore, we are very interested in determining the effects of gray water use on physical, chemical and biological characteristics of the landscape soil. In addition, as these landscape plants will be watered with a drip irrigation system, we will also find out how well such an irrigation system performs and what kind of maintenance it might require when running gray water through it.”
Cabrera said this is the kind of information needed by city planners, water-system administrators, and municipal, county and state officials for the purpose of officially permitting and promoting the use of gray water as a significant urban water conservation practice.
“We hope this also will lead to support by other agencies, groups and organizations, and eventually expand into a statewide initiative to inspire people to use gray water for home landscape irrigation,” he said.