TOTAL COLIFORM BACTERIA PRESENCE/ABSENCE TESTING
Coliforms are a large group of bacteria which commonly live in the digestive tracts of humans and animals. For this reason, coliform bacteria are found in sewage and animal wastes. However, many coliforms are harmless and can be found in other places such as soil. Unfortunately, the tests for coliform bacteria do not indicate their source. The presence of coliform organisms in drinking water indicates a possible contamination by sewage or animal wastes. Sewage and animal wastes contain many disease causing organisms in addition to coliforms. For this reason, disease causing organisms may be present whenever coliforms are found in drinking water.
Most coliform bacteria testing is performed via a “colorimetric” test. A colorimetric test is a test which forms a color. A distinctive color change indicates the presence of Total Coliform Bacteria. Above, on the left, is an example of a drinking water sample which was positive for coliform bacteria. To the right, is a drinking water test that was negative. If a water sample tests positive for coliform bacteria, our microbiology technician will then examine the sample to determine if there is E. Coli present.
When you receive your Total Coliform Bacteria test results, if the Satisfactory box is checked, this means that no coliforms were found in your sample. Proper system maintenance and bacteriological monitoring should be continued routinely to ensure the safety of the water supply.
If the Unsatisfactory box is checked, this means that coliforms were found in your sample. An additional test for E. Coli was performed and reported in the same section. THE PRESENCE OF COLIFORMS AND E. COLI INDICATES THE SYSTEM IS NOT PROPERLY PROTECTED AGAINST CONTAMINATION AND MAY BE UNSAFE FOR HUMAN CONSUMPTION.
When an unsatisfactory test result is received, it is important to identify and correct the source of contamination as soon as possible, since potential health problems exist. Identify the source of contamination by collecting repeat samples and thoroughly inspecting the system. Correct any obvious health problems that are discovered and shock chlorinate the system if needed. Contact your local health department or regional Department of Health office for assistance.
Click HERE to be directed to the Washington State Department of Health’s resource page for positive Nitrate and/or Coliform test results in private wells.
Instructions for Well Disinfection
If your water sample showed bacteriological contamination, DO NOT DRINK THIS WATER. IT MUST BE BOILED FOR 10 MINUTES BEFORE USING FOR DRINKING, BRUSHING YOUR TEETH, MAKING COFFEE, OR IN FOOD PREPARATION SUCH AS WASHING VEGETABLES ETC.
Follow the directions below for disinfecting the well and pipes. Recollect your sample into a sterile bottle provided by Avocet and return to the lab within 24 hours of collection.
- Use one gallon of fresh household bleach (no perfumes: i.e. “lemon scent,” etc.) that contains sodium hypochlorite. WARNING: There are new household bleaches on the market that do not contain any sodium hypochlorite. Read labels carefully and look for bleach that contains sodium hypochlorite as an ingredient.
- Mix the bleach in 5 to 10 gallons of clear water. Pour half of it directly into the well. If possible, pour the remainder in so that the sides of the casing are washed down. To fully distribute the bleached water in the well, run a garden hose down the well and let it run for 5-10 minutes. This will circulate the bleached water from the well, through the hose and back to the well again.
- After the bleach is added, turn on the taps in the house until the odor or taste of chlorine can be detected, then turn off taps. Do the same for all other taps and faucets in the house. If you have a treatment system on your water, you may need to bypass the treatment unit so that it is not damaged by the bleach.
- Allow the bleach water to remain in the well and pipes at least overnight, 24 hours if possible. Turn on the outside taps until the smell of chlorine is no longer detected; then do the same with taps inside the house.
- After about one week of use, submit another sample for analysis.