Testing well water for fruit and vegetable production

Quick facts

  • Water used for handwashing, produce washing and rinsing, frost protection, irrigation, drinking and other uses on the farm should be tested.

  • When testing water, labs look for harmful pathogens such as total generic E. coli. E. coli is an indicator of fecal contamination in your water.

  • It is important to properly collect the water for testing for an accurate result.

Person collecting well water sample.
Let the water run for 3 minutes before taking a sample to ensure you are testing the water from the well.

Testing your farm’s water for the presence of E.coli is an important part of you farm’s food safety plan. Water tests also help you determine a baseline so you know if something has changed in your water.

Salmonella and E. coli are examples of harmful pathogens that can be present in water and cause foodborne illness, making people sick. Water used for handwashing, produce washing and rinsing, frost protection, irrigation, drinking and other uses on the farm should be tested.

How frequently should I test my water?

The frequency of water testing is determined by the source of the water.

Well water should be tested at least one time per year by a certified laboratory at the beginning of the season.

Municipal water does not need to be tested, but a water bill proving that water comes from a municipal source will be needed if your farm is seeking a GAP audit inspection.

Surface water should be tested at least 3 times per season. It should be tested at the start of the season, during peak use, and prior to harvest. Regardless of testing, surface water should be used only with great caution, and applied only with drip irrigation.

The FSMA Produce Safety Rule requires that agricultural water be tested for generic E. coli. Your buyer or organic inspector may ask for other tests, but the basic test to indicate the safety of your water is generic E. coli. It should be 0 for postharvest uses. There are allowances for water used for irrigation purposes. Learn more about water analysis method requirement (PDF) for FSMA Produce Safety Rule.

How to collect water for testing

  • Irrigation water should be collected as close to the source as possible (from the pump or hydrant).

  • Water used for handwashing, washing and rinsing produce and drinking should be collected from the tap.

  • Call ahead to the lab you will use for the testing. The lab will send you collection bottles or whirly bags (separate ones for coliform bacteria and nitrates/nitrites).

  • Follow the directions included with the sample containers.

  • Keep the sample cool and return it within 30 hours of taking the sample.

  • Labs can be private or county-operated.

A complete list of certified laboratories is available from the Minnesota Department of Health.

What do my water test results mean?


Coliform bacteria are everywhere. Water is tested for total generic E. coli as an “indicator bacteria” group. Presence of coliforms in well or municipal water typically indicates that the well or distribution system is compromised in some way, and that surface contamination is present in the water. There may be pathogens in the water that can make people sick and it could be a contamination risk when used to irrigate or wash produce. You want your report to show 0 total coliforms, which are often reported as “less than one.”

Water containing total coliforms should not be used for drinking or washing or rinsing produce.

Depending on the levels, source and how the water is used, corrective action may be needed, including a disinfection procedure for the well. Retest the water after treatment to ensure that water returns to safe levels.

Nitrites and nitrates

Nitrites and nitrates are dangerous for infants and pregnant women. The state Health Risk Limit for nitrate is 10 mg/L (10 ppm) of nitrate-nitrogen. Water with greater levels should not be used for drinking, but can be used for washing and rinsing produce. Repairing your well or constructing a new, deeper well often result in a significant reduction in the nitrate level. The lab results are often combined and will say Nitrite+Nitrate. You are looking for results less than 10.

Michele Schermann, former Extension educator and Annalisa Hultberg, Extension educator

Support for this project was provided to the Minnesota Fruit and Vegetable Growers Association through the Specialty Crop Block Grant Program – Farm Bill, through the Minnesota Department of Agriculture and the USDA – AMS. These institutions are equal opportunity providers.

Reviewed in 2018

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