Fecal coliform bacteria are generally used as indicators of potential water contamination, as these bacteria are found in human and animal feces. Though not harmful to themselves, fecal coliform bacteria indicate the possible presence of other pathogenic bacteria, viruses, and protozoans that line in animal and human digestive systems. The presence of these organisms can make swimming or eating shellfish harvested from contaminated waters a health risk. Because it is costly, difficult, and time-consuming to test for each pathogen organism, water is general tested for just fecal coliform. The test for fecal coliform is a quick and effective method of detecting potential threats to human health.

Sources of fecal coliform contamination include:

• Combined Sewer Overflow (CSO) effluent
• Leaching septic systems
• Domestic and wild animal waste contained in runoff
• Storm runoff

The Narragansett Bay Commission is currently leading a major project to reduce CSO discharges to Rhode Island’s urban rivers and Narragansett Bay.

1. Pour the water sample into the large test tube containing a tablet (3599) until it is filled to the 10 mL line. Don't worry if you overfill or underfill a little.
2. Replace the cap on the test tube.
3. Stand the tube upright, with the tablet flat on the bottom of the tube.
4. Incubate by storing the tube upright, at room temperature, out of direct sunlight, for 48 hours. Store the tubes where the temperature will be fairly constant and between 70° to 80°F. Do not disturb, handle, or shake tubes during the incubation period.
5. Compare the appearance of the tube to the picture on the Coliform chart. Record the result as negative or positive.

   Negative

   • liquid above gel is clear
   • gel remains at bottom of tube
   • indicator remains red or turns yellow with no gas bubbles

   Positive

   • many gas bubbles present
   • gel rises to surface
   • liquid below gel is cloudy
   • indicator turns yellow

negative • good ‡ indicates less than 20 total coliform colonies per 100 mL of water

positive • poor ‡ indicates more than 20 total coliform colonies per 100 mL of water

If your test result is negative, it is not proof that the water is safe to drink. You should always get drinking water tested by a professional lab.

If fecal coliform counts are high (over 200 colonies/100 mL of a water sample) in a river or lake, there is a greater chance that pathogenic organisms are also present. If you are swimming in waters with high levels of fecal coliform, you have a greater chance of developing a fever, nausea or stomach cramps from swallowing disease-causing organisms, or from pathogens entering the body through cuts in the skin, the nose, mouth, or ears.

Some examples of diseases and illnesses that can be contracted in water with high fecal coliform counts include typhoid fever, hepatitis, gastroenteritis, dysentery and ear infections.  

• Drinking Water = 0 FC/100 mL
• Partial body contact = 1000 FC/100 mL
• Swimming = 200 FC/100 mL
• Treated sewage effluent = less than 200 FC/100 mL

Informational Links

Narragansett Bay Commission

Narragansett Bay CommissioN
Combined Sewer Outfall Project