Bacteria in well water

Best for

Homes where coliform bacteria returned after shock chlorination and well repairs, with water that is clear and already treated for iron, manganese and hardness.

Wrong fit

A first positive test calls for shock chlorination and a retest, not a UV purchase. Counts above 1,000 total coliform or 100 fecal coliform per 100 mL need the well fixed first.

Tradeoff

UV kills bacteria in water as it flows past the lamp but leaves no residual in the pipes, and it fails if the water is cloudy, stained or the lamp is old.

What a bacteria result means

It is not practical to test well water for every germ, so labs test for indicator bacteria. The Minnesota Department of Health explains that total coliform bacteria are everywhere on the ground surface but do not usually live more than a few feet into the soil. When they show up in a well, surface water has found a way in, and disease-causing organisms could have come with it.

There are three results you will see:

• Total coliform. A broad group. Most do not cause disease. A positive result means a pathway exists.
• Fecal coliform or E. coli. Penn State Extension says a positive E. coli result is much more serious than coliform alone, because it shows human or animal waste is reaching the water.
• TNTC or confluent. Penn State notes “too numerous to count” or “confluent” growth means the lab could not give an accurate count. Submit another sample.

Coliform problems are common. Penn State cites a 2006 survey of 450 private wells that found coliform bacteria in about 35% and E. coli in about 15%. They are more common in springs and shallow wells, and in wells with a damaged cap or casing. Penn State also found results swing with the weather: fewer than half of positive wells were still positive when retested during a cold, dry spell.

Is it a health risk?

It can be. Minnesota lists diarrhea, dysentery, salmonellosis, hepatitis and giardiasis among the illnesses that disease-causing organisms in water can cause, with symptoms such as diarrhea, vomiting, cramps, nausea and fever. Infants, children, older adults and people with weakened immune systems are at higher risk. The EPA’s health goal for total coliform, including E. coli, is zero, and Penn State says the drinking water standard is that no coliform bacteria be present.

The right response is calm and quick: change your drinking water today, then find and fix the cause.

If your result is X, do Y

For boiling, Virginia Cooperative Extension calls for a vigorous rolling boil for at least one minute. Minnesota says you can go back to drinking the water without boiling once the well has been disinfected and the water no longer tests positive.

How to test

The CDC recommends testing private wells at least once a year for total coliform bacteria, nitrate, pH and total dissolved solids, and testing again if you notice a change in taste, color or smell, after well repairs, after flooding nearby, or when someone in the home becomes pregnant or a child moves in. See how often to test well water.

Use a sterile bottle from a state-certified lab and follow its instructions exactly. Penn State warns that a non-sterile container can introduce bacteria during sampling. Ask whether the lab reports presence or absence only, or an actual count. A count tells you more about how serious the problem is.

Find the cause first

Penn State’s first step after a positive result is to confirm it with a second sample from a certified lab. Then look for the pathway:

• A missing, cracked or loose well cap, or a vent without a screen.
• A casing that ends at or below ground level, or ground that slopes toward the well.
• Cracks or holes in the casing, or wiring conduit that is not sealed.
• Recent pump work, which Penn State lists as a common one-time source.
• A septic system or animal area too close to the well, especially with E. coli.

Minnesota also flags older wells built before modern well codes, and wells too close to septic systems or feedlots, as higher risk. Repairs often fix the problem for good, which is far cheaper than living with a treatment system.

Shock chlorination

Shock chlorination puts a strong chlorine solution through the well and the plumbing to kill bacteria. Minnesota recommends 50 to 200 parts per million of chlorine in the recirculating water and warns that going above 200 ppm reduces effectiveness. Use plain, unscented household bleach, bypass softeners and filters, and do not run the chlorinated water into your septic system. Penn State recommends having it done by a well professional, and Minnesota’s instructions include strict electrical safety steps.

Then retest:

• Penn State: retest about 10 to 14 days later. If clean, test again two to three months later.
• Minnesota: retest two to four weeks after disinfection, because coliform can regrow, and repeat the disinfection if it does.

Set realistic expectations. Penn State found that shock chlorination plus a sanitary well cap removed bacteria for a year in about 15% of contaminated wells, and it worked best where counts were low (under 10 colonies per 100 mL) and E. coli was absent. Minnesota notes it is not unusual to disinfect several times when coliform has been growing in a system for a long time.

When continuous disinfection makes sense

If bacteria return after repairs and shock chlorination, you need treatment that runs all the time. The two common options are ultraviolet light and chlorination.

UV disinfection adds no chemicals. Virginia Cooperative Extension says UV is effective against bacteria and viruses, and that cloudy water or sediment limits light penetration, so UV is usually the last device in the treatment train. Both Penn State and Virginia Cooperative Extension say UV is not recommended where total coliform exceeds 1,000 per 100 mL or fecal coliform exceeds 100 per 100 mL. The lamp weakens with age and must be replaced on schedule.

UV needs clean water ahead of it. SpringWell’s UV spec calls for hardness under 7 gpg, iron under 0.3 ppm and tannins under 0.1 ppm, so many wells need an iron filter or softener first. SpringWell rates its unit at up to 15 GPM for 99.9% of bacteria and viruses, with an annual lamp change. SpringWell’s UV water purification system is one option for recurring coliform once the well is sound and the water is clear. The UV system guide covers sizing and installation.

Continuous chlorination injects chlorine ahead of a contact tank. Penn State notes the water should be clear first, and that iron, hydrogen sulfide and organic matter use up chlorine. It is the better choice when bacteria counts are high or when you also need to oxidize iron or sulfur.

Maintenance

• Replace the UV lamp on the maker’s schedule, typically yearly, and clean the quartz sleeve.
• Keep pretreatment working, since a stained or scaled sleeve blocks UV light.
• Keep testing for coliform at least once a year, even with UV installed.
• Disinfect the plumbing when UV goes in. UV treats water only as it flows past the lamp, so it does not clean pipes that are already contaminated.

When to call a pro or the health department

Call your local or state health department if E. coli is found, if anyone in the home is sick, or if flooding reached the well. A licensed well contractor should handle cap and casing repairs, persistent contamination and wells that need cleaning. Find your state’s well program under states.