Getting rid of coliform bacteria takes three steps in order: shock chlorinate the well and the plumbing, retest after the chlorine has cleared, and find and fix the entry route so it does not come back. Skipping the third step is why so many wells test positive again within months, and continuous disinfection is what covers a route you cannot close.
What a positive result is telling you
Total coliform bacteria are common in soil and surface water and are used as an indicator: their presence means a path exists between the surface and your water, not that anyone is necessarily ill. E. coli in the same sample is the serious result, because it indicates fecal contamination. The EPA notes that private wells are not federally regulated under the Safe Drinking Water Act, so no agency is checking this for you and no one will call if it changes.
Shock chlorination, done properly
Shock chlorination means introducing a strong chlorine solution into the well, circulating it back down through the casing to wet the whole bore, then drawing it through every fixture in the house until each tap smells of chlorine. Leave it standing for the dwell time your state extension or contractor specifies, then flush to waste away from septic fields and vegetation. Half measures leave pockets of biofilm that reseed the well within weeks.
Retest, because chlorine hides the answer
Do not sample while chlorine is still present: it suppresses growth and produces a clean result that means nothing. Wait until the residual has cleared from every tap, then have a certified lab test again, and test a second time some weeks later before declaring the problem solved. A well that clears and then fails again has an ongoing entry path, and the sequence in our well water testing guide is how you document it.
Close the entry route, or install a permanent barrier
Look for the usual culprits: a damaged or missing sanitary well cap, casing that ends below grade, a cracked grout seal, surface water ponding around the head, or a septic field too close and uphill. Fixing the defect is the durable answer. Where the source cannot be eliminated, a continuous disinfection stage such as an ultraviolet purifier fitted after sediment filtration keeps the supply safe every day rather than once.
Questions people ask about how to get rid of coliform bacteria in well water
Is it safe to drink the water while I wait for results?
Use bottled water or boil it until you have a clear retest, particularly if E. coli was detected or anyone in the house is very young or unwell.
How long after shock chlorination should I retest?
Wait until no chlorine smell or residual remains at any tap, then sample. Testing while chlorine is present gives a false clean result.
Will a carbon filter remove coliform bacteria?
No. Carbon treats taste and odor and can even harbor growth. Bacteria need disinfection such as chlorination or an ultraviolet purifier.
Why did the coliform come back?
The entry route was never closed. Check the well cap, casing height, grout seal and surface drainage before shocking the well a second time.