“If you use [drinking water] for something else—say a company uses it as an ingredient or a processing aid—you can’t rely on EPA drinking water rules since the risk assessment on which those rules are based is for a household use of drinking water at less than one illness for 10,000 exposures,” says Posy. “But a household won’t have 10,000 exposures for about two to three years; a food plant will have 10,000 exposures the first day of the month!”
Is Treatment an Option?
Approaches to treating water differ, but for most the principal sticking point for irrigation water treatment is the price. Daniel Snow, PhD, lab director of the University of Nebraska’s Water Sciences Laboratory, argues, “I think monitoring and understanding impacts to irrigation water quality is clearly important, but treatment will be extremely difficult and prohibitively expensive in comparison to monitoring and treating drinking water.”
The difference, says Dr. LaBorde, is the massive volume of water used for irrigation—much of it turbid and full of organic matter.
“It’s not like you can put some chlorine in a bucket of water,” Dr. LaBorde says. “This is thousands and thousands of gallons. But some people have done that: They’ve had systems that run irrigation water through large pellets of chlorine, and it comes out treated. But chlorine isn’t a very good sanitizer for high turbidity water.”
The other question, he notes, is whether treatment is actually practical. Trying to imagine how much sanitizing agent one would need to treat the water for a major leafy-greens farm, Dr. LaBorde comments it simply costs too much, though such an approach might be workable in smaller farms that would not have to invest as much as a major operator to treat the volume of their irrigation water.
“Some people are actually shifting away from surface water and going to well water,” Dr. LaBorde says. “In theory it’s quite a bit less risky because if it’s a good well and it’s maintained, it’s not exposed to the surface and unexpected events and flooding.” Yet wells—which demand access to a potable aquifer—are not always available, Dr. LaBorde notes, while “out in California, they have had a drought. Those wells are getting low, and there’s only so much water.”
Posy, however, believes there is a role for treatment to play in agricultural water safety. “Since chemicals can have disinfection by-products and require serious control to make sure they do not have impact on the produce itself, I’m a fan of UV disinfection,” she says. “Even if you overdose the water, there’s no negative impact downstream. Watering cycles are not 24/7—we need to get smarter about how to employ treatments that are well controlled and portable as well as remotely controlled. There are systems available that treat water by measuring the real-time quality of the water and using only the dose needed, when needed. Integrated reporting means that the machine tracks key parameters and tells you when you need to pay attention. The key is to use validated systems, not just ‘check-the-box’ systems.”
Best Pathogen Practices
There are simply no easy solutions to the questions surrounding irrigation water safety, says the University of Nebraska’s Dr. Snow.
“At the very least, we might consider developing programs to evaluate irrigation water safety in areas with intensive food crop production,” he says, adding, “Regulation is seldom an efficient means for solving complex problems. If regulations governing irrigation water quality are being considered, there should be sound science supporting the type of monitoring and controls to be implemented.”
This is what concerns Dr. LaBorde as well. Above all, he says, we simply don’t know very much about irrigation safety, and many of the practices we’ve attempted to put into place for reducing pathogens are very expensive but may not be proven to reduce contamination risks. For smaller operators, shelling out for testing procedures they’re not even sure will keep their produce safe is a source of resentment.