How do you treat a well after a positive coliform test?
Last updated Reviewed by Sean Mihelich, founder of Save My Well
Find the entry point first, then treat, then retest. Coliform in a well means something is getting in, so walk the wellhead for the usual doorways: a loose or cracked cap, a casing that does not stand clear of ponding water, ground sloping toward the well. Seal the doorway, run a full treatment through the well and plumbing, flush, and retest one to two weeks later. Drink from another source until the retest comes back clean.
Treating a well with a disinfectant is also called shock chlorination.
Treating without fixing the entry point is a treadmill: the treatment clears the water and the doorway lets the next dose of bacteria in. The cap gasket is the cheapest fix in well ownership and the most common answer.
The dose is sized by your well's gallons, from its depth, casing diameter, and static water level. We pull those numbers from your state's official well record and pack the kit to them, with bacteria tests for before and after.
Sources
Oregon State University Well Water Program, Understanding Coliform Bacteria in Well Water, undated
Minnesota Department of Health, Bacterial Safety of Well Water, 2026
Penn State Extension, Shock Chlorination of Wells and Springs, 2025
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