What is coliform bacteria? 

Presence of coliform bacteria indicates water contamination and the presence of intestinal parasites and pathogens in a water supply.  

What are some sources of coliform bacteria?

Sources of these bacteria include runoff from woodlands, pastures, feedlots, septic tanks, and sewage plants.

When and why should coliform bacteria be tested?

Routine testing should be done since coliform bacteria are indicators for pathogens that make people sick. Routine testing for bacteria is highly recommended even if it is not a perceived concerned because annual testing can provide a record of water quality that can be used to help solve future problems. Testing should be done during the spring or summer after a rainy period. Testing should also be preformed after repairing or replacing an old well, or pump. Read more about when you should test your well water for coliform bacteria here


Source:"Chapter 2 - Lakes." Fecal Coliform Bacteria Concentrations. Web. 27 May 2015. 

Source: Centers for Disease Control and Prevention. Centers for Disease Control and Prevention, 7 Jan. 2015. Web. 27 May 2015. 


How can I quickly disinfect my drinking water?

Shock chlorination is used whenever there is a need for emergency disinfection of tanks, wells and/or distribution systems where there is confirmed evidence of microbiological contamination. Shock chlorination disinfects wells use liquid household bleach. If your well is infected with coliform bacteria learn more about shock chlorination of drinking water here

If choosing to perform shock chlorination, use the calculator below to determine how much unscented, 8.25% bleach you should use.

Static water level: water in a well not affected by withdrawal (pumping) of ground water.

How to measure static water level

How can I maintain my well and prevent future coliform infestations?


To learn about septic tank maintenance and further maintenance you can do to help prevent coliform bacteria infection click on the following links:

1) Private Drinking Water Wells (EPA)

2) Well Maintainence (CDC)


Shock clorination intructions

  1. Determine amount of bleach needed using calculator above. Add bleach to 4-5 gallons of water before pouring it into the well.
  2. Mix bleach thoroughly and attached hose to nearest tap, downstream of the well. (tap should be prior to unpressurized storage reservoirs, if not possible contact DWP. Recirculate water by running water back into the sanitary seal that was used to add the bleach. Recirculate for (15-20 minutes)
  3. Open each faucet or plumbing fixture served by the well until 50 ppm of chlorine is detected or until you can smell bleach at each faucet. Close all fixtures and faucets and let sit for 8 hours.
  4. Remove all chlorine to flush from service lines according to DEQ decision matrix for disposal guidelines. Do not dump the water near plants and animals. This procedure should not be used on a daily basis.
  5. Well water for drinking should be tested for arsenic after shock chlorination to make sure water is drinkable.