Jan 17, 2019
Water testing lab search aided by MSU resource

While most of the Produce Safety Rule (PSR) is either in effect or coming into effect in the next year, when it comes to agricultural water, growers have a little more time get into their routine. This is because there have been changes to the types of tests allowed under the rule, but this expansion in available tests doesn’t mean finding the right lab will be easy.

The first consideration in finding a lab is figuring out what kind of water you are using on your farm. Water used for frost protection, overhead irrigation and crop sprays (among other things) is categorized as production water. Any non-municipal water source where the water touches the portion of the plant that is eventually harvested will need to have a quantitative test, or one that generates a number, performed.

Water on the farm used during or after harvest for things like washing, fluming and cooling produce is post-harvest water. This water can either be tested using either quantitative or presence/absence methods.

Production water

When figuring out where you can get your production water tested, consider both the testing methods available at the labs you are looking at, as well as how quickly you can get samples to the labs. For pre-harvest water, the Food Safety Modernization Act’s Produce Safety Rule currently allows nine tests, all of which essentially count (or quantify) the number of generic E. coli in the water. The numbers you receive from these tests will allow you to calculate a geometric mean and build your water quality profile. The tests currently allowed are:

  • Method 1103.1 (mTEC agar)
  • Method 1603 (modified mTEC agar)
  • Method 1604 (MI agar)
  • Method D 5392-93 (mTEC agar)
  • Method 9213 D (mTEC agar)
  • Method 9222 B (m-Endo) followed by 9222 G (NA-MUG agar)
  • Method 9223 B (IDEXX Colilert test kit), with Quanti-tray 2000
  • Method 9223 B (IDEXX Colilert-18 test kit), with Quanti-tray 2000
  • Hach Method 10029 (m-ColiBlue 24 ampules)

Think of a method number like the scientific name of a species. Scientists call corn Zea mays to make sure other scientists are on the same page, and these method numbers are how people deeply involved in water testing refer to the tests. The “common name” of some of these tests are listed above in parentheses.

Select a lab near your farm. For the quantitative tests, you only have six hours from the time you collect the sample until it needs to be at the lab for testing. This means that mailing a sample in is out of the question, or if a local health department sends samples they receive to the state water lab in Lansing, Michigan, it may also take too long.

Postharvest water

For water used in the packhouse or for handwashing, there is a slightly different set of standards. Because the water must start with no detectable E. coli, some presence/absence methods can be used in addition to the methods listed above. These testing methods are:

  • TECTA EC/TC medium and instrument
  • Modified Colitag, ATP D05-0035
  • IDEXX Colilert test kit
  • IDEXX Colilert-18 test kit
  • IDEXX Colisure test kit
  • E*Colite Bag or Vial test
  • Readycult Coliforms 100

For post-harvest water tests, you have a longer time between when a sample is collected and when it needs to be tested. For the seven methods listed above, the hold time is 30 hours, so you have more time to get the sample to the lab.

Finding a lab

To aid growers in finding a local lab, Michigan State University Extension employees have surveyed public and private water testing labs from around Michigan. The information can be found in the map below, which highlights labs that offer the tests allowed by the Produce Safety Rule, as well as other information that can help you reach out to a lab and figure out how to get the water tests you need done. Note, the map is likely to change with time as labs adapt to the rule along with growers.

If you are not currently testing your water, now is a good time to start. It can take time to work out the kinks in your sampling protocol, and knowing what is going on with E. coli in your water and adjusting irrigation accordingly is a good agricultural practice. If you are a grower who has to comply with FSMA, total your produce sales and use the table below to get an idea of when you need to start your FSMA-compliant water testing.

Business size (in produce sales) Year to start testing
All other businesses (>$500K) 2022
Small businesses (>$250K-500K) 2023
Very small businesses (>$25K-250K) 2024

If you are a lab who offers one of the above tests and want to be included on this map for Michigan growers, fill out a form detailing a little bit more about your lab, which will then be added to the map above. The online form can be found at https://bit.ly/MIagwaterlabsurvey. If you are a lab preparing to field these types of calls, see “Farmers growing produce commonly eaten raw will be contacting water testing labs about new rule.”

For more information on on-farm food safety, as well as updates on the Produce Safety Rule and educational opportunities, visit the MSU Extension Agrifood Safety webpage.

–  M and 

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