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Produce Food Safety Midwest Veg Guide 2022 35 Water should be tested for generic E. coli at least annually, or as required by law or individual food safety programs. In general, current guidelines allow an average of no more than 126 colony forming units of generic E. coli per 100 milliliters (CFU/100 ml) of water intended for pre-harvest uses. Water exceeding these parameters may require a corrective action, such as water treatment, inspection and repair of the water system, or extending the time between the last irrigation and harvest. E. coli should be below detectable limits (typically reported as ≤ 0 CFU/ml) for postharvest uses (product cleaning, product cooling, etc.). Water quality laboratories who use the approved FDA methods for testing have been identified across the United States on a map which can be accessed at go.uvm.edu/waterlabmap . Growers covered by the Produce Safety Rule may also be required to meet certain water testing requirements and criteria. For more water sampling information and a summary of Produce Safety Rule water testing criteria, growers should consult Purdue Extension Publication, On-farm Food Safety for Produce Growers: Microbial Water Quality Testing, edustore.purdue.edu . Irrigation Water Pathogens can be introduced into irrigation water through manure runoff from animal production facilities, sewage runoff from treatment facilities or septic systems, or directly from wildlife. Extreme rainfall, manure spills, or human waste can increase the probability of contamination occurring. Ground water is the least likely water source to be contaminated. Well water, when used directly, bears a relatively low contamination risk, provided that the wells are properly constructed and maintained. Wellheads should be protected from contamination by elevating the wellhead above ground level and using backflow prevention devices. Surface water (such as ponds, creeks, and rivers) carries the highest risk for contamination. Microbe levels in surface water may change rapidly. Also, surface water cannot be protected from contamination by wildlife, runoff, or other potential sources of contamination. The following measures may reduce the risk of microbial contamination in surface water: 1. Construct ponds well away from apparent sources of contamination such as livestock facilities and pastures, composting pads, and sewage systems. 2. Fence ponds to prevent wildlife and domestic animals from entering and contaminating the water and surroundings. 3. Redirect runoff to flow away from the pond by building a bank or channel. 4. Establish vegetation buffer zones around ponds to filter runoff before it gets into the pond. 5. If irrigating from a creek or river, consider using a settling pond. This will allow large particles that may contain bacteria to settle at the bottom. 6. Communicate with neighboring livestock producers and work collaboratively to maximize the distance between livestock and water used for irrigation, spraying, or other crop production practices. 7. Sediment and high microbial contamination loads may be washed in by heavy rain. Remember to use caution if using the water source after a heavy rain event. Water application methods (drip, overhead, or furrow irrigation), timing (how close to harvest), and vegetable types (above, below, or on the soil) are also factors to consider. These factors are often interrelated and have to be considered in a combination. Process Water Water is used in many processing (or postharvest) operations, including washing, cooling, top-icing, and transferring product with flumes. Contaminated process water has the potential to introduce and spread contamination throughout an entire harvest lot. Process water that is not of adequate microbial quality can easily transfer pathogens from contaminated to noncontaminated produce. To prevent cross-contamination, sanitizers may be added to process waters. Sanitizers added to process water do not "clean" the product as such. They merely sanitize the water and prevent contamination from one piece of produce from spreading to other pieces of produce. There are a number of chemical and nonchemical (called pesticide devices by FDA) sanitizers, such as chlorine, chlorine dioxide, peracetic acid, hydrogen peroxide, ozone, and UV light. The treatment chosen depends on various factors, such as the type of produce, type of postharvest operation, market requirements, etc. Seek sound technical advice before investing in a sanitizing system. Any chemical treatment used should be labeled for its intended use. See table below for a list of EPA-registered products for use in produce wash water. Growers who use sanitizers should be prepared to monitor water pH, turbidity, temperature, and other factors that affect sanitizer performance. More information about chlorine-based monitoring systems is available in Oxidation-Reduction Potential (ORP) for Water Disinfection Monitoring, Control and Documentation, University of California publication 8149, available from anrcatalog.ucanr.edu . Waste (manure) Growers should use caution when using animal-derived soil amendments. Biological soil amendments of animal origin (BSAAO), those soil amendments such as manure, bone meal, or feather meal, that are animal-derived may contain human pathogens. Growers who use raw manure should insure a lengthy interval between application and harvest. It is