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Shortlist

Contaminant

Bacteria in drinking water

Also listed as Coliform · Total coliform · Total coliform bacteria · Fecal coliform

Microbial contamination, a real risk in untreated wells or compromised supplies.

This page can’t tell you what’s in your tap water.
Only a test of water from your own tap can. Public-system results describe the system, not your home.
7 sources
01Check your water systemWater Check · system results, not your tap02Test your tapHow to get a reliable result03Treatment approachesWhat can reduce it at the tap
On this page · 10 sections
  1. 01Reference values
  2. 02Is it in my water?
  3. 03Where it comes from
  4. 04Testing
  5. 05Water filters
  6. 06Treatment
  7. 07Evidence
  8. 08Next steps
  9. 09Ask about bacteria
  10. 10References
Reference values

No numeric reference held.

Each value says what kind of reference it is, and they mean different things. A lower or missing number never means water is safe.

No numeric reference held

WaterDecoder doesn’t hold a verified reference value for bacteria in drinking water. That doesn’t mean any level is safe. It means we haven’t verified one to show you.

Is it in my water?

Only a test of your own tap can tell.

Choose what you have. We’ll show what it can and can’t tell you.

If you haven’t tested
Nobody can tell without a measurement, including us.

Three things you can do, in this order.

Test water from your tapThis is the only way to know your level. Testing guidance ↓See what your system reportsSystem results aren’t a tap measurement. Open Water Check →On a private well?Public-system reports don’t cover wells. Open Well Water →
Where it comes from

Where it comes from

  1. Found in the environment, foods, water, and the intestines of people and animals
  2. Surface contamination entering water through poorly constructed or damaged wells
  3. Indicator of sanitary protection failure in well and water systems
Why it matters
Can cause diarrhea, urinary tract infections, pneumonia, sepsis, and other illnesses; Shiga toxin-producing strains can lead to hemolytic uremic syndrome with kidney failure, permanent health problems, and death
Infants, children, elderly people, and people with weakened immune systems are more likely to get sick or die from E. coli in drinking water
Testing

How to test your tap water for bacteria

Test water using an enumeration method to count bacterial colonies; retest one to two weeks after any treatment, then monthly for two to three months, and annually thereafter

  1. 01Use a certified labA state-certified lab, or a kit that sends samples to one.
  2. 02Follow the sampling stepsHow and when you collect the water changes the result.
  3. 03Check the reportIt should state units and the detection limit.
Certified labNot sponsored
Use a state-certified labYour state keeps a list of labs certified for drinking water.

Water filters for bacteria

Not offered here
We don’t make picks for disinfection on this page.

This isn’t a function we select products for on contaminant pages.

See treatment systemsRead treatment approaches
Treatment

How to reduce bacteria in water

Function: DisinfectionDisinfection through chlorination kills E. coli and other disease-causing microorganisms in water
How to treat itReducing live bacteria takes a microbiological purifier (UV disinfection under NSF/ANSI 55, or a filter certified under NSF P231) or boiling, not a standard taste-and-odor filter. If you’re on a well, test for bacteria first so you know what you’re treating.
Whole-house systems and point-of-use filters treat different water. A whole-house system treats water where it enters the home; a point-of-use filter treats the tap it’s installed on. Check which one a claim is for.
Evidence

What the evidence means

We keep evidence types apart. A result for one configuration never stands in for another, and we never average across types.

No product in our database holds a reduction record for bacteria yet.

How we read evidence →

Next steps

Take the next step

Match a system to your homeFinder asks about your home first.
Ask about bacteria

Still have a question?

Answers come only from WaterDecoder’s reviewed sources and show citations. Ask can’t interpret your test result or choose a product. Don’t include personal details.

AI assistant

Ask about Bacteria

Answers draw on cited public-health sources and the filters certified to reduce Bacteria. Every source is linked, and if the sources don’t cover a question, the answer says so.

Questions to start with

Educational information from cited sources. Not medical or professional advice.

References

Where these facts come from

  1. 1Knowledge BaseShock Disinfection Chlorination Of WellsWater Research Center
  2. 2Knowledge BaseEmergency Disinfection of Drinking WaterU.S. EPA (Office of Water)
  3. 3Knowledge BaseTotal Coliform and E. coli Bacteria (Well Water Interpreting Results)Montana State University Extension - MSU Well Educated Program
  4. 4Knowledge BaseAbout Escherichia coli InfectionCDC (Centers for Disease Control and Prevention)
  5. 5Knowledge BaseBacterial Safety of Well WaterMinnesota Department of Health
  6. 6Knowledge BaseOverview of Drinking Water Treatment TechnologiesUS EPA (SDWA program)
  7. 7Knowledge BaseGuidelines for Testing Well WaterCDC (Division of Drinking Water Safety)

Written and maintained by WaterDecoder. A review date appears only once we have confirmed one.

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