WCFS - Western Center for Food Safety

Agricultural Water and Soil Amendments

Framework Documents

The Western Center for Food Safety was asked by the U.S. Food and Drug Administration to facilitate the development of research protocols for scientific studies that evaluate the persistence of foodborne pathogens in the environment and on the edible portions of fresh produce following:

  • application of potentially contaminated untreated soil amendments of animal origin to land used to grow fresh produce or
  • application of potentially contaminated agricultural water applied to the edible portion of the crop

Methods used to generate currently available data vary widely and thereby complicate objective evaluation and comparison of data from multiple studies. Two committees of research scientists were established to survey key existing studies and generate recommendations based on their findings. The resulting documents provide a framework for the design of future studies and may be a useful tool for evaluating the strength of existing data.

The Agricultural Water and Soil Amendment framework documents were developed by two committees through a series of webinars, e-mail communication and a workshop that was held in Davis, CA in October 2011. Additional academic, government and industry food safety experts reviewed the draft documents prior to submission to the Journal of Food Protection.

Activity-Specific Food Safety Information


Agricultural Water

Agricultural Water and the Produce Safety Rule

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 E. coli 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 that are representative of use and collected as close to harvest as possible over a growing season or over a period of 1 year. Geometric mean (GM) and Statistical Threshold Value (STV) are calculated from these 4 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 1 new sample. “Rolling” GM and STV values are calculated by combining the old and new sample data. For example, for an MWQP established with 4 samples, one new sample would be combined with the most recent 3 samples from the previous MWQP 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:

Untreated Ground Water:

Links are also available on the UA Fresh Produce Safety website  


Western US Irrigation Water Conference April 24-25, 2014 Summary Report Available

Western US Irrigation Water Conference

The purpose of this summary document is to record the key points and recommendations that were discussed over the course of the conference. We hope that the information contained herein will help stimulate further conversation and consensus on effective strategies to implement the agricultural water quality standards in the Produce Safety Rule. 

Download the summary.