Produce Rule Water Testing Requirements

In January 2016, Standards for the Growing, Harvesting, Packing, and Holding of Produce for Human Consumption, otherwise known as the Produce Rule, became law. This rule, as part of the Food Safety and Modernization Act, sets a standard for produce food safety. Not all growers are covered by the rule. An excellent flowchart to help determine coverage may be found at http://www.fda.gov/downloads/Food/GuidanceRegulation/FSMA/UCM472499.pdf.  Those growers who are covered by the rule will have from 2-4 years, depending on farm size (defined by gross sales), to be in compliance. All growers will then receive an additional 2 years to comply with the water testing component of the rule.

The water testing component of the produce rule requires growers to regularly test irrigation water. Growers irrigating with surface water (ponds, lakes, streams, ditches) are required to collect and test 20 samples over a two-year period in order to establish a baseline. Once the baseline is established, 5 samples must be collected and tested every year thereafter. Growers using underground water sources (i.e. wells) will be required to initially collect and test 5 samples over a one-year period in order to establish a baseline. Once the baseline is established, below ground water sources will need to be tested once annually.

When writing the produce rule, the Food and Drug Administration (FDA) chose to use generic E. coli as an indicator of water quality. Indicators, while not human pathogens, are used to indicate the potential for contamination with a human pathogen. The reasoning is that if the indicator organisms are present, there is a reasonable likelihood that human pathogens may also be present. As a result, water samples collected by growers who are covered by the produce rule will need to be tested for generic E. coli, in addition to any other tests the grower may require.

For all irrigation water, the geometric mean of sample results cannot exceed 126 colony forming units (CFU) of generic E. coli per 100 ml of water. Additionally, the statistical threshold value cannot exceed 410 CFU generic E. coli per 100 ml. In the case of surface water, the initial 20 samples will be used to confirm that the irrigation water meets quality standards. After baseline establishment, growers will use the most current year’s test results (5 samples) and the 15 most recent test results from previous years to create a rolling dataset of 20 test results from which new threshold calculations are performed annually. In the case of irrigation water from below-ground sources, an initial 4 samples will be used to confirm that the irrigation water meets quality standards. After baseline establishment, growers will use the previous year’s test results (1 sample) and the 3 most recent test results to create a rolling dataset of 4 test results from which new threshold calculations are performed annually.

This standard applies to all water applied to the crop prior to harvest. In writing the produce rule, FDA chose not to differentiate between methods of irrigation.  Consequently, the water testing requirement and thresholds apply whether growers utilize drip or overhead irrigation. In cases where growers’ test results exceed the thresholds, the issue must be addressed and corrected. Growers have the following options:

  1. Allowing time for microbial die-off in the field between irrigation and harvest. Growers may assume a 0.5 log reduction per day in microbe levels.
  2. Treating the water or water source with an approved sanitizer
  3. Finding an alternative water source that meets requirements.

Water used for postharvest must be potable, which means no detectable generic E. coli. It is the responsibility of each farm to be able to demonstrate that their postharvest water meets this quality standard. In the case of farms using well water for packing lines or for other postharvest uses, they will need to document that the water is of sufficient quality by having the well tested in accordance with the procedures for underground water. This means collecting an initial four samples over a one-year period, establishing a baseline, and then testing one sample annually. Growers who are using well water for postharvest are advised to begin this process as early as possible in the growing season in order to establish their baseline prior to this season’s harvest. In establishing the baseline, tests from last season may be used, as long as all the tests are taken within a one-year period.

Please feel free to contact me at 812-886-0198 or jsmonroe@purdue.edu should you have any questions about water testing or any other components of the produce rule.

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