Annalisa Hultberg, Extension Educator, Food Safety
If you use well or surface water in the production of your fresh fruits and vegetables, E. coli can be present in water and contaminate your produce or equipment. You might assume your well water is safe, but without testing it, you cannot tell if the well is failing or surface water is getting in. But what do you tell the water lab when you call? Follow this script to help navigate that conversation.
What to test for?
For bacterial contamination, you will want to test for the presence of generic E. coli since this is the best indicator of the presence of fecal contamination in your water. You might add things like lead, arsenic or nitrates/nitrites.
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 $30 - $50 per sample.
Script - how to "speak lab"
- Call ahead to the lab you would like to use. Tell them "I would like to test my agricultural water for quantified generic E. coli. This is agricultural water that will be used for irrigation or postharvest use with fresh produce."
- Note on speaking lab: If the lab employee says "Are you sure you want to test for E. coli? Don't you want to test for total coliform bacteria?" You should say yes, please test for generic E. coli, and tell me how much is in there, not just presence/absence. They are more familiar with testing drinking water (which is only testing for presence of total coliform bacteria), so being asked to test for E. coli is somewhat less common.
Why test for E. coli? The reason is because E. coli bacteria indicates fecal contamination, which is what we are worried about. Total coliform bacteria in water means that there is surface contamination or soil, but not necessarily feces. Test for E. coli to get the best sense of the presence of pathogenic bacteria that can cause human illness. - The lab will send sample collection containers in the mail or you pick them up. Important - determine with the lab how long you have between collection and the lab receiving the sample, and when you can drop them off. They might be closed on Fridays for example, and might not take samples after 3:00 pm to allow for the test time.
- Carefully read and follow the directions included with the sample containers.
- Wash your hands before collecting the sample!
- 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.
- 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.
- Carefully open the sample container, ensuring that you do not touch or otherwise contaminate any interior portion of the container.
- Follow instructions for filling, and do not allow the container to overflow.
- 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 well water sources, generic E. coli should test at less than 1, or not detectable in a 100 mL sample.
For surface water sources, you likely will have total coliforms and generic E. coli present, since this water is much more open to the environment. That is why surface water can only be used for irrigation, and not postharvest uses.
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.
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 use like washing vegetables.
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.
More resources:
Comments
Post a Comment