Annalisa Hultberg Extension Educator, Food Safety
Don't forget one of the most important parts of making sure you are producing safe food this season - testing your water for bacterial contamination. If you have not yet, spring and early summer is a great time to test your farm's water to make sure you have safe water to use all season. Human pathogens, such as Salmonella or 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.
This spring I have heard from two farms who have tested their wells and found that there was detectable total colifom levels in their well. Detectable coliforms in a concentration > 1 MPN/100 ml means that the well is not potable, and action needs to be taken to correct the problem and then make the water potable again. The farms retested, and one found that the second sample came back negative. So, the first time they had touched the inside of the container or not washed their hands, and they had a false positive. That mistake meant they had to pay for the test twice. Read on for tips on how to test your water right the first time to save money and ensure your farm's water is safe.
1.) What are your water sources?
Ground water sources, like wells, tend to be less risky than surface water; however, the risk of contamination is still present in wells, 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.
2.) What to 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.
When you call the lab tell them you have agricultural water, if it is surface or well water, and that you want a quantitative generic E. coli test.
3.) Where to find a lab near you
Laboratories that test 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 $25 - $40 per sample.
4.) How to collect a sample 
Collecting a water sample from a pond for testing
1. Call ahead to the lab you will use for the testing. Tell the lab that you want your water tested for quantified total 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 in the mail or you pick them up.
3. Carefully read and follow the directions included with the sample containers.
4. Wash your hands before collecting the sample! (This is very important!) You do not want a false positive.
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. If you are collected surface water, attach the container to a long pole to reach out into the water source.
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.
Surface water being collected. The farmer taped the bottle to an extension pole to pull a sample from the pond.
How to Interpret the Results
For ground water, both total coliform or generic E. coli should test at less than 1, or not detectable in a 100 mL sample. For surface water, you likely will have some some total coliforms and generic E. coli present. That is why surface water can only be used for irrigation, and not postharvest uses.
If your test indicated the presence of coliforms or generic E. coli in well water, generally this means that the well or distribution system is compromised in some way, and that the water is contaminated.
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.
A water analysis lab takes samples in. Samples must be on ice upon arrival.
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
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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