How to Test for Bacteria in Well Water (Coliform & E. coli)

To test well water for E. coli, you fill a sterile bottle from a cold tap inside the house, keep it cold, and get it to a lab within a day or two. The lab reports two lines, total coliform and E. coli, and each one comes back present or absent. I tell people to skip the store vials for this one and use a lab, either the local water testing lab in your area or a mail-in lab test like ours, because a bacteria result decides whether your family drinks the water.

Caller "The tenant is saying they have E. coli in their water. And I just don't understand what these... it just says detected."

Aidan "Well, it's either present or absent. And if it's present, then it has to be treated."

A property manager in Maryland called me in October with a tenant's report from the kitchen sink. This page is the long version of that answer: how to take the sample, and what the result means.

Lab test or store kit?

For a bacteria result you are going to act on, use a lab. The quick tests at Lowe's or Home Depot "just give you a color to match on a color chart," and with bacteria the answer decides whether you drink the water. Either way, you take the sample yourself at the house.

Our kit's samples go to an ISO/IEC 17025-accredited lab in SimpleLab's network, and I go over the results with you afterward. CDC tells well owners to use a state-certified lab, and your health department keeps the list; if a sale or a lender needs that paperwork, call one of those labs first. For a broader first test of the well, start with how to test well water.

How to take a bacteria sample

A clean sample is most of the test. Kansas State's extension guide puts it plainly: results from "the most meticulous laboratory are no better than sample collection and handling." Michigan's health department warns that bacteria on your hands can get into the bottle and show bacteria that are not in your well. Follow the card that comes with your bottle; these are the steps the state labs give.

1. Use the lab's bottle as it comes

   Do not rinse it. Missouri's instructions say the powder inside "is needed for the sample testing." Some bottles in our kit already contain the preservatives the lab methods need.

2. Pick a cold tap inside the house

   Use one that gets used every day and does not leak. Skip an outdoor spigot, a frost-free hydrant, a swinging spout, and any tap that runs through a softener or a filter.

3. Take the screen off the faucet tip

   Unscrew the screen or aerator from the end of the faucet.

4. Disinfect the end of the faucet

   Wipe it with rubbing alcohol, or spray it inside and out with bleach water (Missouri uses 1 1/2 teaspoons of unscented bleach in a gallon of water).

5. Run the cold water a few minutes

   Missouri says 3 minutes, Kansas State says at least 5. Then turn it down to a slow stream so it does not splash. With our kit, follow the card: one bottle is filled before you run the water and one after.

6. Fill the bottle without touching inside

   Hold the cap by the top and never touch the inside of the cap or the bottle. Hold the bottle by the bottom so water running off your hand does not go in. Fill to the line on the bottle and screw the cap on straight and tight.

7. Keep the sample cold

   Cold, but not frozen: Missouri's lab will not test a frozen sample. Our kit has a cold pack you freeze before you sample, and it rides back with the bottles.

8. Ship the sample the same day

   Fill out the card, put the bottles in the plastic bag, seal everything in the padded foil pouch, and drop it at FedEx the day you collect.

How soon a bacteria sample expires

A bacteria sample has a short clock: EPA's rule for public water systems allows 30 hours from filling the bottle to the lab starting the test, and Missouri's state lab takes private well samples up to 48 hours. That is why the state labs say a sample should never be on its way to the lab over a weekend, and why our kit says to collect on a Monday, Tuesday or Wednesday and drop it at FedEx the same day.

A local lab can usually get a bacteria test done in a couple of days. With our kit, the lab reports about 5 business days after it receives your sample; counting the kit's trip to you and back, most people have results 2 to 4 weeks after they order.

What your bacteria result means

A bacteria report has two lines, total coliform and E. coli, and each one reads present or absent. Some labs print it differently. This is how Michigan's health department reads the common wordings:

EPA's health goal for E. coli in drinking water is zero, so any E. coli in the sample is a failing result. People ask me how much worse E. coli is than coliform. "It's a whole lot worse." Most coliform bacteria live in soil and on plants and generally will not make you sick, CDC says, but they get into a well the same way the germs that do make you sick get in. E. coli comes from human and animal waste; when the property manager asked where it comes from, I said it is usually a leaking septic or farm animals.

It is common. In the tests my customers send in, about 2 in 5 come back with coliform present (200 of 495), and about 1 in 20 with E. coli (23 of 495); every E. coli result also had coliform. North Carolina found coliform in about 26% of the private wells it sampled and E. coli in about 2%.

Could it be a bad sample?

It can be, but don't count on it. When people ask me that, I tell them "it's possible, but the lab gathering instructions and the containers they use are specific, and usually it's right on the money." Missouri's health department suggests a second sample when only coliform shows up, before you do anything else; when E. coli shows up, it says disinfect the well first and test again afterward. If you retest, take it from the same kind of tap, follow every step above, and see how to get rid of coliform bacteria for when a retest makes sense.

Bacteria on your report

Send Aidan a photo of your bacteria report

Text a picture of your report, or the link to it, and Aidan will tell you what it means for your well and what to do next.

Text Aidan443-277-2204 Call800-460-5810Aidan

8 AM to 5 PM Eastern, seven days a week. A real person, not a call center.

What an HPC (general bacteria count) means

A heterotrophic plate count (HPC) counts the ordinary bacteria, yeasts and molds that grow in a water sample, and EPA says HPC "has no health effects." It is not the safety test; total coliform and E. coli are. EPA uses HPC to show how well a public water system is maintained: "the lower the concentration of bacteria in drinking water, the better maintained the water system is."

The 500 you may see next to it comes from EPA's treatment rule for public systems: no more than 500 bacterial colonies per milliliter. EPA's rules do not cover private wells at all, so there is no HPC limit for your well. Two things are worth knowing when the number is high. Above 500 per milliliter, EPA notes, HPC bacteria can get in the way of the lab finding coliform. And a high or rising count can be a sign of biologically active water, such as growth on the inside of a tank. Our well test does not report HPC. If another lab's report shows one, send it to me along with the coliform and E. coli lines.

What to do after a positive test

Stop drinking the water until a retest comes back clean, then deal with how the bacteria get in. Use bottled water for drinking, cooking, ice, baby formula and brushing your teeth, or bring the water to a full rolling boil for 1 minute.

Health departments usually tell you to shock the well with chlorine first and add treatment if the bacteria come back. People call me and say the lab told them to shock the well, and ask if that is enough. "No, it's not enough. Typically, it's a waste of your time." They shock it, it passes, and "a couple of months later, they retested it, and it failed again," because the bacteria are in the aquifer. I tell them to put in a UV light, which goes on the wall where the water comes into the house after the pressure tank. Test for hardness, iron and manganese before you do, because they get in the way of the UV killing the bacteria.

The full steps, including how to shock the well, how long to wait before the retest and how to clean the house pipes, are in how to get rid of coliform bacteria in well water. The lights themselves are on the UV water disinfection systems page.

When to test a well for bacteria

CDC says to test a private well for total coliform at least once every year, along with nitrate, total dissolved solids and pH, and to check the well itself every spring. Test again right away when:

• the well floods, or the water turns cloudy after heavy rain
• any part of the well system is repaired or replaced
• the water's taste, color or smell changes
• someone in the house becomes pregnant, or a child comes to live with you
• people drinking the water get an upset stomach, vomiting, fever or diarrhea

What test buyers wrote

Both are verified purchases of our well test, quoted as written.

Frequently asked questions