The letter (or email) from the lab says it in bold: Total Coliform — PRESENT. Your stomach drops. Your family has been drinking this water. Is it sewage? Are the kids going to get sick? Do you need a new well?
Take a breath. A positive coliform test is the single most common "failed" result in private well testing — and in most cases it does not mean sewage is in your water. It means your well has an opening somewhere that surface water, insects, or soil can get through. That's a fixable plumbing problem, not a condemned well. This weekend, you can find that opening, disinfect the system, and be on your way to two clean retests.
But the answer depends entirely on which result came back positive — so let's read your report properly first.
Total Coliform vs. E. coli: Two Very Different Results
Coliform bacteria are a large family of mostly harmless bacteria that live in soil, on vegetation, and — some of them — in the guts of warm-blooded animals. Labs test for them because they're easy to detect and they travel the same paths dangerous organisms would use. Think of them as the canary, not the poison.
Total coliform present, E. coli absent. This is the common one. It means surface contamination is reaching your well — a cracked cap, a bad seal, a casing that ends below grade, recent heavy rain. The water isn't proven dangerous; it's proven unprotected. Fix the entry point, disinfect, retest.
E. coli present. This is the serious one. E. coli lives in the intestines of humans and animals, so its presence means fecal material is reaching your water — from a septic system, livestock, or wildlife. Stop drinking the water immediately. Use bottled water, or boil water at a rolling boil for one full minute before drinking, cooking, or brushing teeth. Then work the same fix list below — but with urgency, and retest before you trust a single glass.
If you got a "present/absent" result from a basic strip and want lab-grade confirmation with actual counts, the Tap Score Coliform + E. coli Kit mails you a sterile bottle, you overnight it back, and a certified lab reports both organisms — no guessing about whether you swabbed the faucet wrong.
How Bacteria Got In: The 10-Minute Wellhead Inspection
Before any treatment, find the door they walked through — otherwise you'll be shocking the well every six months forever. Walk out to your wellhead and check:
- The cap. Is it cracked, loose, or missing its gasket? Can you rock it by hand? A modern vermin-proof cap with a rubber seal costs about $40 and is the #1 fix.
- The casing height. The casing should extend at least 12 inches above the ground. If your well is in a pit or the casing is at grade, rainwater runs straight in.
- Grading. The ground should slope away from the casing in all directions. A dip around the casing = a funnel.
- The vent and conduit. Vent screens keep insects out. Electrical conduit openings should be sealed.
- Distance from septic. Most codes require 50+ feet between a well and a septic tank or drain field. If your E. coli positive coincides with a soggy drain field, the septic system is the suspect — call a septic professional, not just a well guy.
Note what you find (photos help — you'll want them for comparison next year).
The Fix: Shock Chlorination
Once the entry point is repaired, kill everything that already got in. Shock chlorination floods the well, pressure tank, and every pipe in the house with a strong chlorine solution, holds it overnight, then flushes it out. The short version:
- Pour the calculated bleach dose (or pre-measured well sanitizer pellets) into the well.
- Circulate with a garden hose back into the casing until you smell chlorine.
- Draw chlorinated water to every fixture, hot and cold.
- Hold 12–24 hours with no water use, then flush until chlorine test strips read zero.
We have the full walkthrough with exact bleach amounts by well depth and diameter here: How to Shock Chlorinate Your Well.
Retest — Twice
One clean test after shocking proves the chlorine worked, not that the problem is gone. The standard used by most health departments: retest 1–2 weeks after flushing all chlorine out, then again 2–3 months later. Two consecutive clean results = fixed. A positive on either retest means bacteria are re-entering, and it's time for continuous disinfection.
If It Keeps Coming Back: UV Disinfection
Some wells — shallow ones, dug wells, wells in fractured rock — recontaminate no matter how tight the cap is. The permanent answer is an ultraviolet (UV) purification system installed after your pressure tank. UV destroys bacteria, viruses, and parasites with no chemicals and no change in taste. Two rules: it needs a sediment pre-filter upstream (UV can't zap what it can't see through), and the bulb must be replaced every 12 months even if it still glows — here's why. Expect $300–$700 installed DIY.
Your Action Plan
- Today: Read your report. E. coli present → bottled/boiled water only, starting now.
- Today: 10-minute wellhead inspection. Order the cap, kit, or pellets you need.
- This weekend: Repair the entry point, then shock chlorinate.
- Week 2: Retest. Month 3: Retest again.
- If either retest fails: Price a UV system, sized to your flow rate.
The retest schedule is where this plan usually dies — nobody remembers, and an untested well feels fine right up until it isn't. Log today's result in the WellKept app, record the shock chlorination date, and let it remind you at week 2, month 3, and every year after. When the county or a future home buyer asks for your well's history, you'll be the rare owner who actually has one.
Frequently Asked Questions
Can I shower if my well tests positive for coliform? Yes, for a total-coliform-only result — bathing is low risk for healthy adults as long as you avoid swallowing water. If E. coli is present, healthy adults can still shower cautiously, but young children who might swallow bath water should be sponge-bathed until the well is disinfected and retested.
Will boiling water kill coliform bacteria? Yes. A rolling boil for one minute kills coliform, E. coli, and other bacteria and parasites. Boiling is the correct short-term response while you disinfect the well — but it's a stopgap, not a fix, and it does nothing for chemical contaminants like nitrates.
How did coliform bacteria get into my well? Almost always through a surface pathway: a cracked or unsealed well cap, casing that's too low or corroded, poor grading that pools rainwater at the wellhead, or a nearby septic system. Heavy rain and flooding are the most common triggers because they push surface water past weak seals.
How much does it cost to fix coliform in well water?
Typically $50–$150 for the DIY path: a new vermin-proof well cap ($40), bleach or sanitizer pellets ($20–$30), and confirmation retests. If contamination recurs and you need a UV disinfection system, expect $300–$700 for equipment plus annual bulb replacement (~$60–$100).
How long after shocking a well can you drink the water? Once all chlorine has flushed out (verify with test strips) and a follow-up bacteria test comes back absent — usually 3–10 days after treatment. Drinking heavily chlorinated water is the lesser risk; trusting an unverified well is the bigger one.