Safe use of water is critical in fresh fruit and vegetable production. Water can move harmful microorganisms originating from animal or human feces across a large area or a large volume of product. The water source and how and when the water is applied greatly influence the risk for crop contamination to occur.
Pre-Versus Postharvest Water
When we think about agricultural water and food safety, it is useful to consider the many ways water is used during production, harvesting, and handling fresh produce. Preharvest water is used for crop irrigation, cooling, frost protection, as a carrier for fertilizers and pesticides, and for washing tools and harvest containers, handwashing, and drinking. Postharvest water is used for washing and transporting produce, cooling, applying waxes and coatings, handwashing, and drinking.
Water Source Increases or Decreases Risk
Sources of water used on the farm can be grouped into three types based on the likelihood that they can become contaminated: (1) surface water, (2) well water, and (3) municipal water.
Surface water includes ponds, open springs, lakes, rivers, and streams. It has the highest risk for contamination because we often do not have control over what might be entering the water source upstream at any given time. Access of wild and domestic animals, drainage from upstream cattle operations, runoff from manure piles, and sewage discharges are all possible causes for sudden and unexpected surface water contamination.
Water obtained from the wells on your farm generally has an intermediate risk. The potential for well water to become contaminated with harmful microorganisms is greatest when they are located too close to flood zones, septic tanks, cesspools, animal agricultural sites, manure storage areas, or drainage fields. Risks are greatly increased if the wells have not been constructed properly, or if the well casing has become cracked over time. However, if wells are properly sited, constructed, and maintained, they can be a reliable source of contaminant-free water.
Municipal water obtained from your local water authority has the lowest level of food safety risk. We expect this to be the safest type of water because it is required by law to meet the highest chemical and microbiological drinking water standards, and it is tested regularly to ensure that it is consistently safe to drink.
Peppers and tomatoes are grown here using plasticulture and drip irrigation, which eliminates most of the potential for irrigation water to contact the fruit.
Preventing Agricultural Water from Becoming a Source of Contamination
Postharvest Water: Produce Washing, Handwashing, Cooling, Drinking
- Conduct a potable water test. It is critical to use pathogen-free water for all postharvest water used for washing, flumes and tanks, handwashing, and drinking.
- If postharvest water does not meet the drinking water standard, it may be possible to treat the source with a one-time shock chlorination.
- If postharvest water does not meet the drinking water standard, it may be necessary to install a continuous sanitation system using chlorination or ultraviolet (UV) light.
Surface Water Used for Irrigation (Preharvest)
- Regularly monitor the microbial content of your surface water. Consider testing three times each season:
- At planting
- At peak use
- At or near harvest
- Look for evidence of entry points for animals or areas where runoff can occur. Consider installing fences, vegetative buffer plantings, diversion berms, or other physical structures to protect the water from animal intrusion or drainage from contamination sources.
- When possible, use indirect irrigation methods, such as drip irrigation, that minimize water contact with fruits, tomatoes, peppers, and cole crops.
- Plasticulture methods that cover drip lines provide further protection for lower-growing crops such as leafy greens, cantaloupes, and summer squash.
- Use overhead irrigation in the morning to allow adequate drying of the crop surface before harvest. This speeds the destruction of both human and plant pathogens, and saves water.
- Maximize the time between overhead irrigation and harvest.
- Consider switching to well or municipal water for overhead irrigation and crop spraying methods.
- Monitor your well water quality at least twice during the growing season.
- Check that your well is installed correctly. There should be at least 2 inches of grout maintained between the well casing and the surrounding soil to prevent infiltration of surface water. Because well drilling is not regulated in Pennsylvania, your well may not have the proper casing and grout to exclude surface water contaminants.
- Maintain a 100-foot radius around the well that is kept free from animal intrusion, manure piles, or other contamination sources.
- Install a sanitary well cap to prevent insects or small mammals from entering the well.
- Inspect your wells at least once each year. Check that the well cap and casing seal are in good condition.
Monitoring Water Quality
Regular water testing can give you useful knowledge about the safety of water and how it might vary during the season or from year to year. Water testing labs test for E. coli instead of Salmonella spp., Listeria monocytogenes, hepatitis A virus, parasites, and other sources of human illness because it can be a useful indicator of these and other pathogens.
Growers who sell their produce through wholesale markets may be required to test their water as a condition of sale. Contact your buyers to make sure you understand their testing requirements. The Food Safety Modernization Act will require water testing for produce growers regulated under the law.
Where Can I Test My Water?
Penn State's College of Agricultural Sciences has established a farm food safety irrigation water testing program to facilitate and encourage testing by fresh produce growers in Pennsylvania. Instructions on how to submit a water sample to the laboratory are provided with test kits available from Penn State Extension offices. Several private laboratories in the state also perform E. coli testing on agricultural water. A list of labs may be found in the Penn State Extension website.
Many labs, including the Penn State College of Agricultural Sciences, conduct potable water testing. Make sure to follow water testing directions included in the test kits.
What Standard Does My Water Need to Meet?
Postharvest water used for washing and transporting produce, cooling, applying waxes and coatings, and handwashing and drinking must meet the drinking water standard.
This well has a sanitary well cap and casing done correctly.
The most commonly used microbial standard for preharvest agricultural water (crop irrigation, frost protection, as a carrier for fertilizers and pesticides, for washing tools and harvest containers) is based on the U.S. Environmental Protection Agency (EPA) standards for recreational water. This standard says that you may have no more than 235 E. coli bacteria in a single 100-milliliter sample and that the average for the last five samples can be no more than 126 E. coli bacteria per 100 milliliters. High E. coli levels do not always predict the presence of human pathogens, but they are the only true indicator of fecal contamination and thus suggest conditions where pathogens might be present. It is important that you ask your testing laboratory to provide you with the actual number of E. coli bacteria in your sample, not just a confirmation of whether they are absent or present.
It is important to test the quality of water from surface water sources used for irrigation or other agricultural uses.
Prepared by the Penn State Extension Farm Food Safety team; Tianna DuPont, Penn State Extension; and Luke LaBorde, Penn State Department of Food Science. Reviewed by Thomas Ford and Lee Stivers, Penn State Extension. 2015