How to test Total Coliforms using the IDEXX Colilert 2000 method
What is it? Total coliform is the sum of all coliform bacteria found in the water, including both fecal and non-fecal bacteria found in a 100mL sample of water.
Why is it important? Total coliforms include fecal bacteria like E. Coli and Enterococci and other non-fecal coliforms. While these are naturally occurring, they can make us sick if we ingest them in our drinking waters or are exposed to them while swimming or engaging in other recreational water activities.
What does it mean? Measuring total coliform can help us determine what activities are safe. Total coliform is measured in a lab, and it takes 24 hours to get your results. The lab gives you special containers and teaches you how to make sure your sample isn't contaminated.
Safe levels:
- less than 1 coliform/100mL: Safe for drinking
- under 100 coliforms/100mL: Safe for swimming
- under 200 coliforms/100mL: Safe for fishing and boating
- above 200 coliforms/100mL: AVOID!
How to test
The IDEXX colilert test quantifies both total coliforms and Escherichia coli in water samples, with results in 24 hours. When used in combination with a Quanti-tray system, counts of the bacteria can be recorded.
Sample collection:
- Wearing gloves, collect a water sample in a bottle or Whirl-pak bag.
- Place the sample in a cooler to prevent further bacterial growth
Lab processing:
- Add the colilert reagent to the water sample and mix thoroughly
- Pour the water sample/reagent mixture into the Quanti-Tray 2000.
- Seal the tray with the Quanti-Tray sealer
- Place the sealed tray in an incubator at 35°C ± 0.5°C incubator for 24 hours
- Note: dilution may be necessary
Read the results:
- Count Yellow wells = total coliforms
- Count Yellow/fluorescent wells = E. coli
- Report and share the data