The Produce Safety Rule (PSR) requires growers to initially establish a Microbial Water Quality Profile (MWQP) for each untreated surface agricultural water source used during growing activities of covered produce (other than sprouts).
The Produce Safety Rules (PSR) must be applied for each water source using a direct water application method and annual surveys must be conducted for that water source in subsequent years.
The water quality profile is based on the levels of generic E. coli in your agricultural water using 100mL sample sizes. The method of testing for generic E. coli must be conducted following U.S. Environmental Protection Agency (EPA) Method 1603. Methods other than 1603 may be used but they must be scientifically valid and shown to be at least equivalent to EPA Method 1603 in accuracy, precision, and sensitivity.
Some experts have stated that testing water samples with 100mL sample size is not sufficient and may not detect pathogens if they are at very low levels.
Research led by the Centers for Disease Control and Prevention is examining a new irrigation water sample collection and testing methods that are expected to enable better detection of pathogens and fecal organisms other than E.coli for irrigation water. Ultra filtration water sampling techniques seem to be offering better options for risk assessment. The technique involves robust filters with minute pours that can trap bacteria, parasites and viruses. A battery powered portable pump is used to filter water from rivers, lakes or ponds at rates of 2 to 4 liters per minute.
Agricultural water is defined in part “as water that is intended to, or likely to, contact the harvestable portion of covered produce or food-contact surfaces.”
Geometric Mean (GM): GM is essentially the average amount of generic E. coli in your water source. FSMA Produce Safety Rule criteria requires a GM at or below 126 E. coli CFU/100mL.
Statistical Threshold Value (STV): STV is a measure of variability of generic E. coli levels in your water source. In simple terms, it is the level where 90 percent of the samples (log values) are below the value. Produce Safety Rule requires an STV at or below 410 E. coli CFU/100mL.
CFU (colony forming units) is the estimate of bacterial concentration in your water per 100mL.
More information on the Produce Safety Rule and agricultural water can be found here:
http://www.fda.gov/Food/GuidanceRegulation/FSMA/ucm334114.htm
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