Annalisa Hultberg Extension Educator, Food Safety
Human pathogens, such as Salmonella or pathogenic E. coli, can be present in water used in the water you use for irrigation and postharvest uses like handwashing and rinsing vegetables, and can make people sick if ingested. Testing your water annually for bacteria is an important way to protect your customers from potential illness associated with contaminated water.
Collecting a water sample Photo credit: Jules Geisler
What is the risk of different water sources?
Surface waters like ponds are considered the highest risk to produce safety since their quality can be highly variable and they are susceptible to contamination from animals and other sources.
Livestock can contaminate surface water Photo Wes Kline, Rutgers University
Ground water sources, like wells, tend to be less risky than surface water; however, the risk of contamination is still present, especially in older wells or those near animal feeding areas. There can be hairline fractures in your well’s casing, rodents or other animals living in the well head, missing or broken well caps, incorrect grading or other reasons why your well water might become contaminated. All water sources on the farm, regardless of type, should be tested.
What should I test for ?
There are different tests you can ask the laboratory to run, depending on your use and requirements. For most farms, it is best to test for the presence of generic E. coli since this is the best indicator of the presence of fecal contamination in your water.
GENERAL POTABILITY TESTS
Potability tests for well water usually include nitrate/nitrate and total coliforms. Total coliform is an indicator organism used to determine whether or not the water source had been contaminated. Potable water should have no detectable total coliforms; often reported as “less than one” or “absent”. This test is one way to meet GAP audit requirements.
GENERIC E. COLI
As part of the FSMA Produce Safety Rule as currently written, farms covered by the rule are required to test water for generic E. coli, an indicator organism specific to fecal contamination, rather than for total coliforms. It is best to ask for a “quantitative” or “enumerated” test for generic E. coli.
Find a lab near you
Laboratories that test drinking water quality may be private or public, such as county-operated. A complete list of certified labs is available from the Minnesota Department of Health here. The tests average about $30 - $40 per sample.
How often should I test?
Well water should be tested at least 1 time per year at the beginning of the season. However, more frequent testing can help you establish a baseline for your water quality. Consider testing at the beginning of the season, at the start of harvest, and again during the peak of harvest.
Surface water should be tested frequently, 3 to 5 times per season. Consider testing at planting, during peak irrigation, and near harvest. Follow best practices to minimize risk such as using drip (rather than overhead) irrigation, and not irrigating immediately prior to harvest. Untreated surface water should never be used for hand washing or postharvest applications.
Municipal water does not need to be tested, but a water bill proving that water comes from a regulated (or managed) municipal source might be needed for GAP audits.
Water Sample Container Photo: Jules Geisler
How to collect a sample
1. Call ahead to the lab you will use for the testing. Tell the lab that you want your water tested for total coliforms or generic E. coli, and that it is agricultural water that will be used for irrigation or postharvest use with fresh produce.
2. The lab will send sample collection containers.
3. Carefully read and follow the directions included with the sample containers.
4. Wash your hands before collecting the sample.
5. Collect water as close to the source as possible, such as at the wellhead or pump. You might also choose to occasionally collect a sample from the end of the distribution system to confirm there is not contamination within the lines.
6. Clean the faucet with dilute bleach or alcohol to remove any potential contamination. Then, let the water run for 5 minutes, or as indicated by the instructions, to flush stagnant water. Let the water run longer if testing further from the source.
7. Carefully open the sample container, ensuring that you do not touch or otherwise contaminate any interior portion of the container.
8. Follow instructions for filling, and do not allow the container to overflow.
9. Keep the sample cool, such as in a cooler on ice, and return it to the lab within the specified time frame; usually 6-30 hours.
How to Interpret the Results
For most ground water, both total coliform or generic E. coli should test at less than 1, or not detectable in a 100 mL sample.
If your test indicated the presence of coliforms or generic E. coli, generally this means that the well or distribution system is compromised in some way, and that the water is contaminated.
This water does not meet requirements for potability, and should not be used for drinking, handwashing, washing produce, or other postharvest uses until the problem is addressed and the water is retested.
Depending on the results, water source, and how the water is used, actions such as well disinfection may be needed. After determining the cause of contamination and correcting it, well disinfection can be done by hiring a licensed well contractor. You can also do it yourself using chlorine bleach. Be sure to follow guidelines from the Minnesota Department of Health. Retest the water after treatment to ensure it has returned to safe levels.
More resources:
If your farm is covered by the FSMA Produce Safety Rule, see the factsheet Testing Water for FSMA Produce Safety Rule.
For more information on the FSMA Produce Safety Rule and if the rule applies to your farm, see the factsheet FSMA and the Produce Safety Rule.
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