Coliform Bacteria - The Global Water Sampling Project

Coliform Bacteria

Background Information
If coliform bacteria are present in the water supply it is an indication that the water supply may be contaminated with sewage or other decomposing waste. Usually coliform bacteria are found in greater abundance on the surface film of the water or in the sediments on the bottom.

Fecal coliform, found in the lower intestines of humans and other warm-blooded animals, is one type of coliform bacteria. The presence of fecal coliform in a water supply is a good indication that sewage has polluted the water. Testing can be done for fecal coliform specifically or for total coliform bacteria which includes all coliform bacteria strains and may indicate fecal contamination.

Test Procedure
Depending on the level of your students and your experience with this type of test, you may opt to do a total coliform test or a fecal coliform test. The total coliform test is simpler but does not give a quantitative result; the test just indicates the presence or absence of coliform bacteria (yes/no).

If a fecal coliform test is performed, please report your results as number of fecal coliform colonies per 100 ml sample of water.

What to Expect
The presence of coliform bacteria may be an indication of a polluted water supply but it would be necessary to do further tests in order to identify the specific bacteria present and the level of contamination.

Recommended fecal coliform bacteria counts are:

Drinking water less than 0 colonies per 100 mL sample of water
Swimming less than 200 colonies per 100 mL sample of water
Boating/Fishing less than 1000 colonies per 100 mL sample of water