What Causes Coliform to Get in Well Water?

Laurie Brenner

Water wells that aren't deep enough -- or protected from water that flows on top of the ground or near the surface -- can easily be contaminated with the coliform bacteria. These bacteria are found everywhere in nature: in soil and plants, and in the intestines of humans and animals.

A half covered well with a bucket.

Water in a well not constructed to modern standards can be vulnerable to coliform contamination.

Poorly Constructed Wells

In earlier times, wells and springs usually consisted of nothing more than a hole dug in the ground, sometimes lined with rocks or bricks and covered with a board, if that. These types of wells and springs, along with shallow wells or wells inside pits, become receptacles for bacteria washed into them during rainy seasons.

Contamination Causes

Coliform can get into well water as a result of flooding; missing or broken well caps, or construction with improper well materials; broken well casings; and contaminant leaks outside of the well casing. Flooding usually happens during the rainy season in wells with heads situated belowground in pits. Older wells made of concrete, rocks, brick or clay do not keep groundwater from seeping into the well, which can lead to coliform contamination.

Test the Water

The only way to tell if your well water has coliform or E. coli, a subgroup of the fecal coliform group, is to have it tested. The best time to test for coliform is right after the rainy season or during early summer. A water testing professional can take a sample of the water in a sterile container and send it to a laboratory for a test for multiple bacteria strains. Though most forms of coliform do not cause disease, types of it -- such as certain forms of E. coli -- can cause serious illnesses. If you have farm animals such as chickens, cows, pigs or sheep and an old hand-dug well or spring near their pasture, chances are your water may contain coliform bacteria, including E. coli.

Boil the Water

When your well tests positive for one of three types of bacteria -- E. coli, total coliform and coliform -- until it can be repaired, modified or a new well dug that meets safety standards, you need to boil water to kill the bacteria. The North Carolina Health Department says to boil the water for at least 1 minute before using it to cook with or drink. While you can chlorinate the well as a temporary solution, you must test for the bacteria after chlorination. And chlorination does not address the underlying problem of well contamination.