Study Finds Recycled Water Safe for Use on Turf Grass

Maintaining high-quality turf grass during the hot Texas summer requires irrigation that increases demand on potable water supplies.

But new Texas Agricultural Experiment Station research found few adverse effects when recycled water was used on grass in the Edwards Aquifer recharge zone. The finding is significant, researchers say, because it could help reduce daily demands from the diminishing aquifer.

The study examined Type 1 recycled water, known as municipally treated wastewater, reclaimed water or effluent water. It's frequently used to irrigate large turfgrass areas, helping to save higher-quality surface and groundwater for potable water use.

With San Antonio's growing population requiring more water, maximum withdrawal rates have been imposed by the Edwards Aquifer Authority.

"One impetus for our study was the fact that two plants and a distribution pipeline have been built to produce and distribute recycled water throughout the metropolitan area," says Jim Thomas, Experiment Station scientist.

Officials questioned whether customers on the recharge zone could use recycled water for irrigating grass. Water officials' main concern was whether unwanted nitrates would penetrate the recharge zone and threaten drinking water.

"We found there were only slight increases in nitrates," Thomas says. "We found it was reasonably safe to use on the location we studied. We had only a slight increase in the accumulation of salt and sodium in the soil."

Results also revealed a slight increase in potassium in leaf tissue and "a little increase in salt leaching down to the groundwater table," he says. "The majority of constituents remained within drinking water requirements. Thus, irrigation with recycled water wasn't going to pose a significant threat to groundwater."

Thomas, who partnered on the study with Experiment Station scientist Richard White, says Type 1 recycled water receiving the highest treatment is rated safe for incidental human contact.

The two-year study began in March 2002 and involved 18 field plots. Irrigation treatments included potable water and recycled water applied at rates to replace evapotranspiration. In addition, the study included recycled water applied at a rate of 1.1 times the rate of evapotranspiration.

Tifway Bermuda grass and Jamur Zoysia grass, common in the San Antonio area, were irrigated in the study. Samples of runoff water, leachate water and soil and leaf tissue were collected monthly and tested for nine nutrients and total salts.

Both water sources were found to be capable of producing high-quality "aesthetically pleasing turf," Thomas says, when combined with proper mowing, fertilizing and other appropriate management practices.

He cautioned that careful long-term salt management would be needed to prevent the accumulation of excessive salts or sodium in the root zone.

"Concentrations of all other nutrients in the soil were unaffected by irrigation water resources," Thomas says.

The study was published in the July-August issue of Agronomy Journal.