Israel: Gastrointestinal diseases not caused by using recycled ‘gray water’ for irrigation

Researchers at Ben-Gurion University’s Zuckerberg Institute for Water Research say treated gray water is safe for irrigation and does not pose a risk for gastrointestinal illness or water-related diseases.

The study, published in the online journal Science of the Total Environment (Elsevier), determined that there was no additional incidence of gastroenteritis or water-related diseases caused by use of treated gray water in gardens, even at the same time as compared to tap water and other irrigation water sources.

Gray water includes any wastewater generated in households or office buildings except for toilet wastewater.

“There is a growing interest in gray water reuse from sinks, bathtubs and washing machines, particularly in water-scarce regions. New gray water systems, inclunding one developed at the Zuckerberg Institute, presently make reuse economically feasible on both a national and household scale, provided it is handled responsibly to eliminate potential environmental and health risks,” researchers said.

The Health Ministry told The Jerusalem Post: “Raw gray water contains a high concentration of pathogenic microorganisms, and with direct irrigation may cause disease, but at the same time as treated properly according to the 2010 regulations, it can be used for agricultural irrigation.”

The ministry added that, “there is no reason for wide use of gray water given the existing health dangers and due to the fact that Israel is the world’s leading country in water recycling, with most of it treated and returned for use in a systematic way.”

However, in those places where there is request for the use of gray water and it is supervised and controlled the ministry said it allows such utilization under the necessary conditions.

Study participants – gray water users and a control group that did not use gray water – were required to complete a weekly health questionnaire for a year, inclunding a preliminary lifestyle questionnaire to assess their exposure level to gray water or potable water used in garden irrigation.

“This study showed that there was no additional incidence of gastroenteritis found part treated gray water users and practically no difference in the prevalence of water-related diseases between gray water and potable water users,” stated researcher Amit Gross. “In fact, the rate of illnesses was found to be lower with the treated gray water than from the control group at times, suggesting that the major exposure to gastrointestinal disease-causing bacteria is likely not from exposure to pathogens in gray water.”

The second study component compared the findings to published results of health risks determined by Quantitative Microbial Risk Assessment (QMRA), a standard process used for measuring the risks from exposure to known microbial pathogens or indicators in water or food sources.

“Since the concentration of pathogens in the current study was higher than QMRA risk levels, from presently on the prevalence of water-related diseases between control and gray water users was similar, we believe that QMRA can be used as a conservative benchmark toward establishing regulations governing gray water reuse,” Gross said.

Following this initial study, Gross recommended further research involving a larger people to strengthen the study’s statistical power and to enable elaboration on the possible connections between gastrointestinal illnesses and exposure to gray water.