carrier of human pathogens to fresh produce. These pathogens could include enteric organisms such as pathogenic E. coli and Salmonella , as well as Listeria monocytogenes . Sources of pathogens may include direct contact with animals, contaminated water run-off from a nearby animal operation, or wildlife into surface waters. While surface waters are known to be the highest risk of all water sources, growers continue to use surface waters because it is likely the most practical and economical option.
Evaluating Water Quality: Use of Microbial Water Quality Profiles, Microbial Water Criteria, and Corrective Measures
Because of known microbial hazards, water used for growing purposes that meets FDA’s definition of agricultural water includes specific requirements to reduce the risk of contamination. These requirements include maintenance and assessment of water sources and distribution systems, as well as the development of a microbial water quality profile by enumerating the indicator organism, E. coli . For agricultural production water from a surface or ground water source, the Produce Safety Rule establishes water quality criteria where each source of production water must be tested to evaluate whether its water quality profile meets the following criteria: 1. A geometric mean of 126 or less colony forming units (CFU) of generic E. coli per 100 mL of water, 2. A statistical threshold value (STV) of 410 CFU or less of generic E. coli per 100 mL of water. Water testing can provide information to help reduce the microbial risks to the grower’s commodity. By testing their water, growers may understand the long-term quality of a water source. This information can then be applied to better determine appropriate uses for each water source. Most importantly, by understanding the microbial quality of water, growers will know when to apply corrective measures if the microbial water quality profile exceeds numerical criteria as required by the Produce Safety Rule. The number of tests will depend on the water source. Table 2 lists the required testing for each water source.
Table 2. Testing Requirements for Water Sources
Source
Testing Requirement*
Public Water Supply
Copy of test results or current certificates of compliance
4 or more times during the growing season or over the period of a year 1 or more samples rolled into profile every year after initial year
Ground
20 or more times over a period of 2 to 4 years 5 or more samples rolled into profile every year after initial survey
Surface
*With appropriate documentation, there is no requirement to test water that meets the requirements for public water supplies. *Profile samples must be representative of use and must be collected as close in time as practicable to, but before, harvest.
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