How dangerous is E. coli in well water?

E. coli in drinking water is a serious health risk. The strain E. coli O157:H7 can cause hemolytic uremic syndrome (HUS), which may lead to kidney failure. Most healthy adults recover from E. coli infection without serious complications, but infants, elderly people, pregnant women, and immunocompromised individuals face higher risk of severe illness. There is no safe level of E. coli in drinking water.

How did E. coli get in my well?

E. coli comes from fecal matter, whether animal or human. Common entry points include flooding that carries surface runoff into the well, a cracked or poorly sealed well casing, a failing septic system too close to the well, or livestock waste upgradient from the well. Surface water finding its way into the well through poor grouting is another common cause.

Can I shower if my well has E. coli?

Healthy adults can generally shower in water with E. coli without significant risk, since skin is a barrier. But avoid getting water in your eyes, nose, or mouth. Don't use the water for brushing teeth, cooking, or making infant formula. Young children should avoid bathing in contaminated water if possible, since they're more likely to swallow water.

How long does it take to fix an E. coli well?

Shock chlorination takes about 24 hours of contact time, plus flushing. After that, you should wait 1-2 weeks before retesting. If the cause was a one-time event like flooding, one round of shock chlorination often resolves it. If you get a second positive test, the problem is structural, and you need a plumber or well contractor to inspect the casing, cap, and seal.

Does boiling water kill E. coli?

Yes. Boiling water at a full rolling boil for 1 minute kills E. coli and other bacteria. At elevations above 6,500 feet, boil for 3 minutes. Boiling is a short-term fix while you treat the well and wait for retest results. It doesn't fix the source of contamination.

E. coli in Well Water: What It Means and What to Do

Health disclaimer: This page provides general information about E. coli contamination in private wells. It is not medical advice. If you or a family member shows symptoms of waterborne illness, contact a healthcare provider immediately.

If anyone in your home develops sudden severe diarrhea, bloody stool, vomiting, or signs of dehydration after drinking well water, contact a doctor immediately. Infants, elderly people, pregnant women, and people with weakened immune systems are at greatest risk of serious illness from E. coli.

A positive E. coli test result on your well water means one thing: fecal contamination is getting in. That’s not a gray area. E. coli doesn’t occur naturally in groundwater. When it shows up, waste material from an animal or human gut has found a path into your water supply.

You need to stop drinking the water and act on this today.

What a Positive Result Actually Means

Most well water tests check for two things: total coliform and E. coli.

Total coliform is a broad indicator. It covers a large group of bacteria found in soil, plants, and animal digestive systems. A positive total coliform result is a warning sign. It means a contamination pathway exists, but many coliform bacteria are harmless on their own.

E. coli is different. It’s a specific type of coliform that lives in the intestinal tracts of warm-blooded animals. Finding it in your well means fecal material is reaching your water. That’s the more serious finding.

There is no acceptable level of E. coli in drinking water. The EPA sets the limit at zero. Any confirmed positive requires immediate response.

The severity varies by strain. Most E. coli strains cause gastrointestinal symptoms that healthy adults recover from in a few days. But E. coli O157:H7 can cause hemolytic uremic syndrome (HUS), a condition that can lead to kidney failure. The CDC tracks HUS as a marker for severe E. coli exposure. Children under five face the highest risk from this strain.

Don’t wait to see if anyone gets sick. Act on the test result.

How E. coli Gets Into Wells

E. coli doesn’t travel far through undisturbed soil. When it shows up in a well, there’s almost always a structural reason, a path that bypassed the natural filtration of soil and rock.

Flooding is the most common acute cause. When floodwater surges across a property, it carries surface runoff, sewage, and animal waste. If a well casing isn’t sealed and elevated above flood level, that water gets in. After Hurricane Helene in 2024, testing of private wells in the storm’s path found contamination in roughly 40% of sampled wells.

Other common entry points:

A cracked or deteriorating well casing that lets surface water seep in at depth
Poor or absent grouting around the casing at the time of drilling
A loose or broken well cap that allows insects, small animals, or rainwater to enter
A septic system too close to the well, or one that’s failing
Livestock pasture upgradient from the well, especially after heavy rain
Agricultural land where manure is applied near the well head

Well age matters. A well casing that was in good shape 30 years ago may have cracks or gaps now. Many older wells were drilled when standards were looser, and their construction wasn’t designed for the long term.

Stop Using the Water. Do This Now.

Don’t use the water for drinking, brushing teeth, cooking, or making infant formula. Switch to commercially bottled water immediately.

If anyone consumed the water before the test result came back, watch for symptoms over the next one to three days: diarrhea, stomach cramps, nausea, vomiting, and sometimes fever. Most healthy adults improve without treatment. If symptoms are severe, especially bloody diarrhea, ask your doctor right away.

For food prep that used the contaminated water, use common sense. Cooked food that reached proper internal temperature is generally fine. Raw rinsed produce, infant formula made with tap water, or beverages mixed with tap water are higher concerns.

The first treatment step is shock chlorination. The EPA’s standard procedure:

Find your well’s approximate water volume. Your driller’s log has the casing diameter and depth.
Add unscented household bleach (5.25% sodium hypochlorite) at roughly 1 quart per 100 gallons of water in the well.
Run water briefly through every tap inside and outside to circulate the bleach through the pipes.
Let the chlorinated water sit for 12 to 24 hours.
Flush the well by running outdoor hoses until you can no longer smell chlorine. Avoid flushing large volumes into your septic system at once.
Wait one to two weeks, then retest before resuming normal use.

For a full step-by-step guide, see How to Shock Chlorinate a Well.

During the treatment and waiting period, use bottled water. Boiling kills E. coli and is a reasonable backup when bottled water isn’t available. Bring water to a full rolling boil for at least one minute before using it.

When to Worry About a Second Positive Test

If you shock chlorinate and retest two weeks later and the result is still positive, the problem isn’t a one-time contamination event. Something structural is allowing ongoing entry.

At that point, you need a licensed well contractor or plumber to inspect the physical well. They’ll check:

The well casing for cracks or gaps
The grouting around the casing
The well cap and seal
The distance and condition of any nearby septic components

Repair might mean regrouting, replacing the cap, lining the casing, or in worst cases, abandoning the well and drilling a new one. That’s expensive, but continuing to drink from a well with recurring E. coli contamination isn’t safe.

A second positive result is also a signal to look harder at your site. Is there a new agricultural use upgradient from your well? Has a neighbor put in a livestock operation? Has your septic system been serviced recently? The structural inspection and site assessment go together.

Long-Term Protection

Once you’ve resolved the acute contamination, a treatment system gives you an ongoing safety net, especially if you’re in a flood-prone area or near agricultural land.

UV disinfection is the best long-term option for bacterial protection. A UV system rated NSF/ANSI 55 Class A inactivates 99.99% or more of bacteria, viruses, and protozoa as water passes through a UV chamber. It adds no chemicals, leaves no taste, and requires minimal maintenance beyond annual lamp replacement.

Class A is the designation that matters. Class B systems are supplemental only and aren’t appropriate as a primary disinfection method.

UV systems don’t work alone. They require pre-filtration because turbid or colored water blocks UV light and reduces its effectiveness. Most installations include a sediment filter and a carbon block filter upstream of the UV unit. UV also doesn’t address chemical contaminants like nitrates, arsenic, or iron. If you have those as well, you’ll need additional filtration.

For vetted UV system options, see Best UV Water Purifiers.

Continuous chlorination is the other approach. A chemical feed pump doses chlorine into the water line before a contact tank. A carbon filter downstream removes residual chlorine before it reaches your taps. It works well, but it requires more attention than UV: monitoring chlorine feed rates, maintaining the pump, and changing carbon media.

For most homeowners, UV is simpler and more hands-off.

Whatever you choose, test your well at least once a year. E. coli contamination can come and go with seasonal flooding, changes in nearby land use, or gradual deterioration of well components. Annual testing, documented over time, is the clearest picture of what’s actually in your water.

For lab testing options, see Best Mail-In Water Tests.

Sources:

U.S. EPA, Private Drinking Water Wells: https://www.epa.gov/privatewells
U.S. CDC, E. coli: https://www.cdc.gov/ecoli/index.html
NSF International, NSF/ANSI 55: Ultraviolet Microbiological Water Treatment Systems
U.S. EPA, Bacteria in Drinking Water: https://www.epa.gov/ground-water-and-drinking-water/ground-water-rule

Health disclaimer: WaterAnswer.com provides general information only. This content does not constitute medical advice. If you suspect waterborne illness, contact a healthcare provider. For emergencies, call 911.