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UC Food Safety
University of California
UC Food Safety

Agricultural Water

The Produce Safety Rule (PSR) requires growers to initially establish a Microbial Water Quality Profile (MWQP) for each untreated agricultural water source used during growing activities of covered produce (other than sprouts) using a direct water application method and conduct annual surveys for that water source in subsequent years. The water quality profile is based on the levels of generic Ecoli in your agricultural water. There are different requirements for agricultural water that comes from surface or ground (well) sources.

More information on the Produce Safety Rule and agricultural water can be found here:
www.fda.gov/Food/GuidanceRegulation/FSMA/ucm334114.htm

Untreated Surface Water:

The initial MWQP must be established with a minimum of 20 water samples that are representative of use and collected as close to harvest as possible over a period of at least 2 years to a maximum of 4 years. Geometric mean (GM) and Statistical Threshold Value (STV) are calculated from these 20 samples (minimum). The GM and STV are your MWQP and should be compared to the microbial quality criteria provided in the Produce Safety Rule.

After the initial MWQP has been established, GM and STV values must be updated annually based on a minimum of 5 new samples. “Rolling” GM and STV values are calculated by combining the old and new sample data. For example, for an MWQP established with 20 samples, five new samples would be combined with the most recent 15 samples from the previous MWQP to update the MWQP and confirm that the water is still being used appropriately.

Untreated Ground Water:

The initial MWQP must be established with a minimum of 4 water samples collected as close to harvest as possible over a growing season or over a period of one year. Geometric mean (GM) and Statistical Threshold Value (STV) are calculated from these 4 samples. The GM and STV are your MWQP and should be compared to the microbial quality criteria provided in the Produce Safety Rule.  After the initial MWQP has been established, GM and STV values must be updated annually based a minimum of 1 new sample. “Rolling” GM and STV values are calculated by combining the old and new sample data. The one new sample combined with the most recent 3 samples from the previous MWQP are used to update the MWQP and confirm that the water is still being used appropriately.

Tools to calculate Geometric Mean and Statistical Threshold Value:

Several tools were developed to make it easy to calculate the GM and STV and to determine if your water meets the criteria for appropriate application to produce before harvest. The tools were also designed to assist you with making water management decisions if your water does not meet the criteria in the Produce Safety Rule.

Untreated Surface Water:

The above links are also available on the UA Fresh Produce Safety website 

Untreated Ground Water:

Additional information:

Interim guidelines on health-related water quality standards for water actually used tor irrigation on Quality control of wastewater for irrigated crop production (FAO, United Nations)

Site Creation date 6/1/2009
Webmaster for site:  Zann Gates

Webmaster Email: zgates@ucdavis.edu