How to Keep Agricultural Water Safe

Consumer preferences for fresh rather than processed produce and vegetables over the past 20 years are causing government regulators and scientists to direct more research toward assuring water used in agriculture is clean.

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Water is the main contributor to transporting pathogens, especially post-harvest, says Luke LaBorde, PhD, a professor of food science at Penn State University in State College, Pennsylvania. Among other work, Dr. LaBorde focuses on Good Agricultural Practices training.

“The closer to the consumer’s mouth, the higher the consideration is of the quality of water used in agriculture,” notes Dr. LaBorde. “Even insects can transfer bacteria sources of contamination from the field to the consumer.”

Agricultural water proposed standards are covered under the Produce Safety rule in the FDA’s Food Safety Modernization Act (FSMA). The proposed rule establishes testing frequency, microbial limits, and remedial methods.

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If pathogens are detected, a farmer may stop using water from a particular source, for example using well water instead of surface water, Dr. LaBorde says. Or, the farmer can treat the water with sanitizer or change watering to a drip irrigation system where only the roots and not the plant leaves are exposed to water.

Municipal water is the safest, followed by ground water in wells. Surface water in canals and streams is subject to fouling by wildlife. The main risks for produce are runoff, the water source, and animal droppings. So while surface water can be used in a drip irrigation system, for example, it may not be good for washing produce after harvest, when well or spring water is best, says Dr. LaBorde.

Farmers also need to be aware of what is upstream from them. For instance, they need to be aware if a new dairy operation has been set up or if a summer home with a faulty septic system is back in use.

AI and Algorithms

Martin Wiedmann, PhD, Gellert Family Professor in Food Safety at Cornell University in Ithaca, New York, is taking a high-tech approach to managing surface water use and to identify when water is at increased risk of having pathogens. He and his colleagues are developing algorithms and mathematical approaches to minimize risks.

Managing surface water is a hot issue, says Dr. Wiedmann.

“One day the water at a certain point may be pathogen free and the next, it may not,” he explains. “The effect of rain can depend on what the land upstream looks like, whether it has farms or weekend houses with old, failing septic systems. So the water may be okay Monday through Friday, but not Saturday or Sunday.”

Dr. Wiedmann is using a GPS map to characterize what is happening upstream from a farm to predict higher or lower risk and to help farmers decide when to treat water or use an alternative source.

He says the FSMA rules are generic, but his approach is precision agriculture based on algorithms and using artificial intelligence to make predictions about water quality in specific areas on specific days.

“FSMA is one size fits all,” he says. “This [ours] is a better way to manage water quality. We’ll take precision agriculture to precision food safety at the field level.”

In the western United States, water conservation also figures into the picture. Researchers at the University of California, Davis, are studying the quality of tailwater, irrigation runoff from a field into a reservoir or pond, for reuse in pre-irrigation and germination.

“It’s very rare to detect pathogens in tailwater,” says Michael Cahn, PhD, farm advisor, irrigation and water resources at UC Davis’ Division of Agriculture and Natural Resources in Salinas, California. His group has been testing five reservoirs and ponds in the Salinas Valley over the past year to evaluate the food safety risks of using tailwater for irrigating leafy green crops using conventional irrigation and production practices. They checked the chemical, physical, and microbiological characteristics of tailwater and well water, looking at nutrients, pH, salinity, dissolved organic carbon, E. coli, coliform bacteria, and Salmonella.

They found that tailwater from the fields did not present more risk than well water despite containing more nutrients and dissolved organic compounds. The group also discovered that generic E. coli survived longer in well water than in tailwater. The survival of pathogenic E. coli and Salmonella in soil and on lettuce leaves was similar for tailwater and well water. Their final report will be published by the Center for Produce Safety.