How to test for total coliforms using the IDEXX Colilert method
What is it? Coliforms are a group of bacteria. Some live naturally in soil, plants, and surface water. Others, like E. coli, come from the poop of animals and people. Total coliforms means all of them counted together in a 100 mL water sample.
Why does it matter? Most coliforms won't make you sick on their own. But if they show up in your water, it's a warning sign that poop may have gotten in — and poop can carry germs that do make people sick. That's why we test for them.
What does it mean? The Colilert test measures total coliforms and E. coli at the same time, which is helpful because E. coli is the more specific indicator for health risk. Once you enter your results, we'll colour-code them based on the standards for your region and the type of water use, so you can see at a glance whether your water falls within safe levels.
How to test
The IDEXX Colilert test measures both total coliforms and E. coli in a water sample, with results in 24 hours. Paired with a Quanti-Tray, it gives you a count using a Most Probable Number (MPN) table from IDEXX.
Sample collection:
- Wearing gloves, collect a water sample in a sterile bottle or Whirl-pak bag.
- Place the sample in a cooler to keep bacteria from multiplying before you get to the lab.
Lab processing:
- Add the Colilert reagent to the water sample and mix until dissolved.
- Pour the mixture into a Quanti-Tray 2000.
- Seal the tray with the Quanti-Tray sealer.
- Incubate at 35°C ± 0.5°C for 24 hours.
- Note: dilution may be needed for samples you expect to have high bacteria counts.
Read the results:
- Yellow wells = total coliforms
- Yellow wells that also glow under UV light = E. coli
- Count the positive wells of each colour and use the IDEXX MPN table to get your result per 100 mL.
- Enter your results into the platform — we'll show you how they compare to the standards for your region.