Demystifying Agricultural Production Water Testing under the FSMA Produce Safety Rule

Defining Agricultural Water?

Under the Food Safety Modernization Act (FSMA) Produce Safety Rule (PSR), agricultural water is defined as “water used in covered activities on covered produce where water is intended to, or is likely to, contact the harvestable portion of the crop” (FDA, 2015).

Covered activities refer to activities described in the FSMA PSR: growing, harvesting, packing and holding of covered produce.

Covered produce refers to produce that is typically consumed raw, and is a raw agricultural commodity. FDA has a list of produce non-covered by the rule; www.fda.gov/media/107445/download.

What is Production Water?

Production water is agricultural water used during produce growing activities prior to harvesting. Examples of production water include irrigation, fertigation, spray applications, dust abatement, frost protection, among others. Remember production water has to meet the definition of agricultural water to be regulated under the FSMA PSR.

This document and its contents refer only to production water under the FSMA PSR and not to harvest or postharvest water.

Why Test your Production Water?

Since microbes are not visible to the human eye, it is impossible to evaluate water quality without testing. Testing each water source, such as wells, ponds, creeks, etc. allows you to understand  the  microbial  quality  of  each source, determine appropriate uses for each source, and implement corrective measures if water does not meet microbial quality standards (PSA, 2019).

It is important that when you test your water, you need to get a number (in other words quantitative testing); not presence/absence.

What to Test your Production Water for?

To be compliant with the FSMA PSR, a farm’s production water that meets the definition of agricultural water, needs to be tested for generic Escherichia coli (FDA, 2015).

Generic E. coli is used as an indicator of fecal contamination (PSA, 2019). The presence of generic E. coli in a water sample does not indicate pathogen contamination, however the levels of generic E. coli in a water sample indicate the microbial quality of a water source, where larger values of generic E. coli may indicate a potential contamination issue.

Water testing under the FSMA PSR requires a 100 mL water sample per water source.

Remember to ask for a quantitative generic E. coli test, where the lab will provide the number or estimation of generic E. coli in the water sample. It is important to obtain a count of generic E. coli for production water samples, as some generic E. coli in a sample is possible.

A test for the presence/absence of generic E. coli will not provide you with the flexibility to evaluate your water quality, as a positive generic E. coli result does not indicate if only a few E. coli or hundreds of E. coli are in a water sample.

How to Sample your Production Water?

It is important to find a laboratory to analyze your water sample(s) before you start. Each laboratory will provide specific instructions for water sample collection and handling including the maximum hold time (the time between collection of a water sample and delivery to the laboratory).

A list (see references for link) has been compiled of laboratories in Virginia who perform water testing to satisfy the FSMA PSR (VDACS, 2018).

For a detailed, step-by-step procedure on how to collect production water samples from both groundwater and surface water sources, see Virginia Cooperative Extension publication “Sampling Agricultural Production Water” (Vallotton et al, 2019).

Also, refer to our instructional video on YouTube (see references for link) demonstrating the water sampling process for ground water and surface water sources (Ling et al, 2017).

How to Interpret your Production Water Test Results?

Remember, for production water, the count of generic E. coli is the target metric. Total coliforms will always be higher than generic E. coli in a water sample (unless both are below the limit of detection) because generic E. coli are a kind of coliform. The count you receive for total coliforms includes generic E. coli and several types of other bacteria. Total coliforms are important because they are used as an indicator in the EPA drinking water standard.

FOLLOWING ON THE NEXT PAGE is a sample water test result from one of the Virginia Department of Agriculture and Consumer Services (VDACS) laboratories. In this example, three water sources were sent for testing: water from a well (A) and water from two surface water sources (A & B).

The VDACS laboratory uses the IDEXX Colilert-18 and Quanti-Tray/2000 (standard method 9223B), therefore, the results will display the most probable number (MPN) of total coliforms and generic E. coli per100 mL water sample. Since we are interested in the FSMA PSR, production agricultural water testing, we only need to focus on the generic E. coli number.

Example Interpretations for Water Sample Result Sheet (on Next Page)

Well water sample A has zero detectable generic E. coli or a result of <1 MPN/100 mL water. This test result supports the water source being of good microbial quality. Laboratories will not report a test of zero; instead, laboratories only report the limit of detection (or lowest amount detectable for the test). This is important to remember when looking at water test results.

Surface water sample A has 10.9 MPN/100 mL water of generic E. coli. This test result also supports the water source being of good microbial quality. Continue sampling this water source to demonstrate long-term water quality as outlined by the FSMA PSR.

Surface water sample B has 524.9 MPN/100 mL water of generic E. coli. This test result does not support the water source being of good microbial quality. While water test results may vary due to natural fluctuations in the environment including weather events, this result should trigger further investigation into determining the root cause of the evaluated level of generic E. coli in the water sample. This means assessing possible causes for the evaluated generic E. coli in the water, and performing any interventions/corrective measures. Once you have investigated and hopefully solved the issue, the water source should be re-tested to check that the corrective measures worked.

References and Resources

Food and Drug Administration (FDA). 2015. Food Safety Modernization Act Produce Safety Rule. https://www.govinfo.gov/content/pkg/FR-2015-11-27/pdf/2015-28159.pdf

Produce Safety Alliance (PSA). 2019. Produce Safety Alliance Grower Training. Module 5, version 1.2. https://producesafetyalliance.cornell.edu/curriculum/

United States Department of Agriculture (USDA). 2011. Good Agricultural Practices and Good Handling Practices Audit Verification Program User’s Guide. https://www.ams.usda.gov/sites/default/files/media/GAPGHP_Audit_Program_User%27s_Guide%5B1%5D.pdf

Virginia Department of Agriculture and Consumer Services (VDACS). 2018. Agricultural Water Testing Labs for FSMA-Produce Safety Rule Requirements. https://www.vdacs.virginia.gov/pdf/producesfty-watertestinglabs.pdf

Vallotton, A., E. Ling, and L Strawn. 2019. Sampling Agricultural Production Water. Virginia Cooperative Extension (VCE) website: https://www.pubs.ext.vt.edu/author/v/vallotton_amber.resource.html

Ling, E., L. Strawn, and A. Vallotton. 2017. How to Sample Untreated Agricultural Water. https://www.youtube.com/watch?v=Vvwj44MJyzc&t=206s

Suslow, T. 2002. Eliminate Fecal Coliforms from Your Vegetable and Fruit Safety Vocabulary. http://postharvest.ucdavis.edu/files/269366.pdf

Virginia Produce Food Safety Website. 2017. http://www.hort.vt.edu/producesafety/