U.S. Water News Online
YUMA, Ariz. -- The water that just washed your clothes may end up being used to keep your grass green in the near future.
It all depends on testing that a University of Arizona researcher in Yuma is doing to see if "gray water" from laundry can be recycled as irrigation water.
The objective was to determine whether children playing on grass wet from watering with gray water would be at risk of picking up pathogens that could make them sick, said Jorge Fonseca, vegetable specialist at the UA Yuma Valley Experiment Farm.
Another objective was to determine the impact of gray water on soil, he said.
What he learned is that the research "is worth pursuing," he said.
"Our project so far has shown us that gray water from laundry does not increase the amount of aerobic bacteria and coliform bacteria in grass or vegetables," he said.
In some cases the laundry gray water from volunteer households has fewer microbes and coliform than water from the irrigation canals, he said. In fact, he added, in some cases, the gray water has fewer pathogens than the canal water. It may even be as safe as tap water.
And the water savings would be substantial, he noted.
"There's a potential to save 45 gallons of water a day per person using all sources of gray water," he said. "There are estimates that 60 to 65 percent of average household water use is gray water."
That includes not only laundry water but also wastewater from such sources as showers and kitchen sinks.
However, in the study, only laundry water was included because of concerns the other sources might have more pathogens, Fonseca said. For example, kitchen water might include juice from raw meat that could be a health hazard.
"I think gray water exclusively from laundry machines is a pretty good way to save thousands of gallons of water a year," he said.
Currently, some Tucson households and 3,000 families in Maricopa County are using gray water to irrigate their lawns, he said.
State and federal regulations recommend that edible plants not be irrigated with gray water. But the description of these regulations vary from state to state and many are vague, "so we still wanted to look at how much risk there is," Fonseca said.
One concern, he said, is that if someone were sick, those pathogens could contaminate the gray water. A collaborative study from Florida found that bacteria in the gray water form a biofilm -- like what people might see lining their kitchen sink -- that is hard to kill.
"So the implication is that we need to be careful if someone is sick," he said.
As for the soil, one concern is the sodium in the detergent, he said. "Excessive accumulation of sodium in soil results in compacted soil that makes it very hard for roots to grow."
Another issue is that stored gray water can develop a sulfur-type odor. Ironically, when one starts smelling this is when the microbial population, including potential pathogens, diminishes. The odor is caused by the anaerobic bacteria converting sulfites from the detergents into hydrogen sulfide, he said.
These preliminary results are positive, but Fonseca and other UA researchers are wary about getting too excited.
"We can't be as confident with our results as they pertain to the soil. Some scientists have proposed that the soil will deteriorate in nutritional make-up after watering with gray water. We have not yet observed the results from our last evaluation, but we believe that even if there is some potential deterioration of soil properties, the amounts of gray water someone may use on their plants will not be enough to erode the soil significantly," Fonseca explained.
He feels that in a typical situation, gray water would provide no more than 10 percent of all the water used to irrigate a lawn or garden. Additional watering with tap water could wash the excess salts deposited from the gray water, he said.
Also, applying gypsum will help prevent most soil deterioration, he said.
The potassium in some detergents actually is beneficial to plants, he said.
Future UA research will include more examination of the effect of gray water on different types of soil and soil exposed to different conditions.
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