“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.