by: Tay Fatke, CFSA’s Local Produce Safety Coordinator
Efficient water-use, decreased labor and operating costs, reduced disease pressure, decreased runoff and erosion are a few of the benefits of using drip irrigation widely known throughout the produce industry. However, a lesser-known benefit of implementing drip irrigation on your farm deals directly with minimizing your food safety risks and may contribute to passing your GAP Audit.
When it comes to on-farm food safety, irrigation water is and always will be a main concern. An important aspect of an on-farm food safety plan includes a water system risk assessment for irrigation water that takes into consideration the historical testing results of the water source, characteristics of the crop, stage of the crop and the method of application.
Out of these considerations, you have the most control over the method of application to your crops. Drip irrigation methods or those where the water does not contact the edible portion of the crop are less likely to be a source of potential contamination. Irrigation methods where the water contacts the edible portion of the crop can be the most risky for causing contamination, especially if surface water (ponds, streams or other open water sources) is used, and therefore the quality of the water fluctuates and needs to be tested at least three times annually for most GAP Standards. In some cases, to ensure the quality, water may need to be treated when coming into direct contact with the edible portions of the crop.
So how can implementing drip irrigation directly help mitigate food safety risks? When water contacts the edible portion of the crop such as overhead sprinkler irrigation, 235 MPN’s (Most Probable Number per 100 mL) or CFU’s (Colony Forming Unit per 100 mL) E. coli is the highest allowable limit. When water does not contact the edible portion of the crop, through the utilization of drip irrigation, 576 MPN’s (Most Probable Number per 100 mL) or CFU’s (Colony Forming Unit per 100 mL) E. coli is the highest allowable limit. Therefore, if you have had past issues with the quality of your water source, switching to drip irrigation will give you that extra cushion of allowable generic E. coli. That being said, it is important to inspect your surface water source after a high sample is received since the geometric mean of the past five water tests, regardless of the method of application, needs to meet 126 MPN’s (Most Probable Number per 100 mL) or CFU’s (Colony Forming Unit per 100 mL) E. coli.
Why do we test for generic E. coli? E. coli is a member of the fecal coliform group and therefore can be used as an accurate indicator of the presence of fecal contamination, which is the primary contamination source in water. Monitoring for generic E. coli can determine the potential for irrigation water to contain fecal contamination. Feces can carry human pathogens that lead to foodborne outbreaks in produce. The pathogens that are associated with feces include pathogenic E. coli, Salmonella, Cryptosporidium, hepatitis A and Norovirus. E.coli detection methods have greatly been improved over the years making this test more affordable, faster results than other specific pathogen testing. Therefore, detection of generic E. coli indicates the possible presence of these pathogens and the amount of generic E. coli found in a water test indicates the usability of that irrigation water.
What does the future hold? Another important consideration is that food safety requirements and interpretations are very fluid, meaning that what is allowable now may potentially not be in the future due to an outbreak of produce linked to contaminated overhead irrigation water, or new scientific evidence from research to support other testing frequencies or methods. Therefore, the safest practice you can do, especially with produce that is normally consumed raw, is to irrigate using drip tape, ensuring water does not come into direct contact with the edible portion of the crop and test your water at required frequencies.
What resources are available to help implement drip irrigation on the farm? Check with your local NRCS and/or Soil and Water office to see if cost-share assistance is available and right for your operation to cover costs for setting up drip irrigation.
If you have additional questions pertaining to irrigation, water quality, or general food safety, contact the Local Produce Safety Initiative staff at CFSA.
Tay Fatke, Local Produce Safety Coordinator – email@example.com
Trish Tripp, Local Produce Safety Manager – firstname.lastname@example.org.
 Refer to the specific GAP Standard for water testing requirements. The agricultural water compliance dates have been extended by the FDA until further scientific evidence of testing frequencies is determined. Small farms and very small farms will have until January 26, 2023, and January 26, 2024, respectively with all other farms coming into compliance by January 26, 2022.