How to Remove Coliform Bacteria from Well Water (Treatment Guide)

If your lab report says total coliform is present, stop drinking the well water today. Use bottled water, or water brought to a rolling boil for 1 minute. You can still shower in it as long as nobody swallows it. Present means something from the surface has a way into your well, and the bacteria that make people sick can use the same way in. Below is what I tell people to do next: when a shock with bleach makes sense, why it usually comes back, and the fix that stays fixed.

Caller "We were trying to buy a house. We received the water test back, and it says microbiology, total coliform. ... It just says present. ... It just says fail."

Aidan "It's either absent or present, or pass or failed. So it means you have coliform bacteria in the water. You can chlorinate the well, but usually it comes back after the chlorine dissipates from the system, and you run it all off."

A buyer partway through a house purchase called me with that report in September. This page is the long version of that answer.

What your coliform result means

Coliform bacteria are a large group that lives in soil and surface water, and most of them will not make you sick on their own. Labs test for coliform because finding it means a path exists from the surface into your water, and the germs that do cause illness can travel the same path. You can't see it, you can't smell it, you can't touch it, so the lab report is the only way you find out. Usually the report just says present or absent, pass or fail, not a number.

E. coli on a well report is usually not the strain from the news stories. Washington's health department says a present result probably is not O157:H7, but it does mean recent fecal contamination, and boiling kills every form of it. If bacteria still show up after a second shock, CDC's advice is to call your local health department.

Should you retest first?

Mississippi State's extension service puts a retest first, because the first bottle may have picked up bacteria while it was being filled. If you retest, take the aerator, filter or hose off the faucet, wash your hands, don't touch the inside of the bottle or the cap, and use the faucet closest to the well or a different one from last time. Ask for E. coli on the retest too. Timing matters: Penn State found bacteria are easiest to find after several weeks of rain and hardest to find in cold, dry weather.

While you wait, look at the well cap. Penn State recommends a tight, sanitary cap that keeps insects and surface water out, a casing that sticks up above the ground, and ground that slopes away from it. When the buyer at the top of this page asked me where it was coming from, I said it could be as simple as bugs that got down the well casing and decomposed, or "it could be in the aquifer, and you'll never know where it came from. It could come from miles away."

Is coliform common in well water?

Yes. Of the 363 well water tests my customers sent in from April to September this year, about 4 in 10 came back with total coliform present (148), and 14 of those also had E. coli. When the USGS sampled private wells across the country, 34% had total coliform.

Report in hand and it says present

Text me a photo of your report

Send the whole report, not just the bacteria line. I'll tell you whether it's a shock, a UV light, or something that has to come out of the water before a UV light will work.

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

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

Using your water until it tests clean

Don't drink it, cook with it or brush your teeth with it, but showers and laundry are fine as long as nobody swallows the water. That is Pennsylvania's health department guidance for coliform, and it holds until a retest comes back clean.

If anyone in the house has had stomach trouble, see a doctor and mention the water test. Pennsylvania's health department lists stomach cramps, diarrhea and vomiting, along with fatigue and fever, and says infants, children, older adults and people with weak immune systems get sick more easily.

How to shock chlorinate your well

Shock chlorinating means putting enough unscented household bleach down the well to kill the bacteria in the well and the house pipes, letting it sit at least 12 hours, then flushing it all out. It is the standard first step in the state guides, and a lot of well drilling companies will recommend it. CDC, Penn State and Mississippi State all recommend having a well or pump contractor do it. Here is what they do, so you know it was done right.

Those are CDC's amounts for unscented household bleach, which runs 5 to 9% on the label. The well pipe is the casing, the pipe that sticks up out of the ground at the well. The number that matters is the depth of the water standing in it, not the total depth of the well. Pennsylvania's environmental agency lands in the same place: about 1 1/2 quarts for 100 feet of water in a 6 inch well.

1. Put your water filters on bypass

   Chlorine this strong can damage some softeners and filters, so turn their bypass valves before anything else. A caller who was just starting to shock his well asked me about his iron filter, and I told him, "I would bypass it. You don't wanna put all that concentrated chlorine in there. It probably wouldn't hurt it, but just to be safe."

2. Mix the bleach in a bucket of water

   Pour the amount from the table into 3 to 5 gallons of water in a clean 5-gallon bucket.

3. Pour the bleach mix down the well

   With the power to the pump turned off, take off the well cap and pour the mix in, keeping it away from the wiring. Then turn the pump back on.

4. Run a garden hose back into the well

   Connect a clean garden hose to the outside faucet closest to the well and run the water back down the casing to mix it, rinsing the inside of the casing for 5 to 10 minutes.

5. Open every faucet until you smell bleach

   Go through the house, hot and cold, and open each faucet until you smell chlorine, then shut it off.

6. Leave the bleach in at least 12 hours

   Don't use any water. CDC says at least 12 hours; a lot of well drillers let it sit 24.

7. Drain the bleach water outside

   Run a hose from an outside faucet onto the driveway or gravel, not the lawn, a garden, a stream or a pond, until the bleach smell is gone. Then run the faucets inside until they don't smell either.

8. Run bleach water through your filters

   A caller in August told me he and his wife had both come down with diarrhea before a test found coliform. He shocked the well and the whole house with his iron filter and softener bypassed, then worried the bacteria were hiding in them. I told him to run bleach water through them until he could smell it at the kitchen sink, let it sit for an hour, and then rinse it out.

9. Wait 7 to 10 days to retest

   CDC says to wait at least 7 to 10 days, once every trace of chlorine is flushed out, and to keep using bottled or boiled water until the result comes back. If it's clean, test again in 2 to 4 weeks and again in 3 to 4 months.

Why coliform comes back after shocking

A shock kills the bacteria that are in the well that day, but it does not close the path they came in on, so for most wells the coliform comes back. Penn State followed contaminated wells that were shock chlorinated and given a sanitary well cap, and the bacteria stayed gone for a year in about 15% of them, mostly wells with low counts and no E. coli. That is why I told the buyer at the top of this page that it usually comes back.

The people who call me after a shock tell the same story. A caller in September runs a well for a small trailer park: "We treated it ... 3 times now. Once last year, and it tested good. And then we did it 2 times this year, just got done, and the test came back positive again." A buyer wrote the same thing in 2020:

"We had coliform in our water tests. We ended up chlorinating our water supply three times but it was still there." Lois H., Apr 2020 Verified buyer

A shock does its job when the bacteria got in once and the cause is gone. Penn State names those cases: a new pump, work on the well, or unusually heavy rain. If it comes back after that, Penn State's own advice is a system that disinfects the water all the time. Fixing a cracked casing or a shallow well is a job for a licensed well driller, and it is worth having one look even if you go straight to a UV light.

A UV light is the permanent fix

A UV light kills the bacteria in every gallon as it passes through on its way into the house, so it keeps working even if you never find where the coliform gets in. It kills E. coli and fecal coliform too. In the video below I explain it in under 3 minutes.

The UV light is a steel chamber with a crystal tube inside it (VIQUA calls it the quartz sleeve), and the UV lamp sits inside that tube. As water passes through the chamber around the crystal, those UV rays disrupt the structure of the DNA of the bacteria, rendering it dead. It mounts on the wall after your well tank, and it goes last, after any iron filter or softener, with a 5 micron sediment filter ahead of it. You change the bulb every 12 months.

The crystal has to stay clean. As I told a caller in September, if it gets coated with iron or scale buildup, "the intensity of the bulb drops and it's useless." VIQUA's limits are under 7 grains of hardness and under 0.3 ppm of iron, and that catches a lot of people: about half of the coliform wells my customers tested this year were also over 7 grains (70 of 147 with a hardness result). The full list is in what to filter out before the UV light. One more limit: Penn State doesn't recommend a UV light when total coliform is over 1,000 colonies per 100 mL or fecal coliform is over 100. If your report gives a count that high, text me before you buy one.

The one I recommend most often for a house is the Viqua VH410, rated 18 gallons a minute at VIQUA's standard dose. For a smaller house, the VH200 ($895) is rated 9; which size fits your house walks through the choice. We recommend a licensed plumber for the install, and I told the buyer at the top of this page it shouldn't take a decent plumber more than an hour.

"Had it installed by local plumber. Working awesome and our water is free of coliform and every other bacteria." Steve C., Mar 2020 Verified buyer

If you are putting in a UV light anyway, I tell people they don't need to shock the well first, because everything that goes through the UV is treated. The state guides still put the shock first, and with E. coli on the report you should follow them. Either way, the pipes after the UV have to be cleaned once it's in; see clean the house pipes after the UV.

The other permanent option is a chlorine injection system, and I steer people away from it: "You have to have multiple pieces of equipment. You have to inject the chlorine, then you have to take it back out with a carbon tank," and "you have to service it on a monthly basis." We don't sell them. The side-by-side is in UV disinfection vs chlorination.

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Test your hardness before you buy a UV

One certified lab test, mailed to you, run by an accredited lab, reports total coliform and E. coli along with the hardness and iron a UV light depends on. If your report already has hardness and iron, skip this.

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Clean the house pipes after the UV

A UV light only treats water on its way into the house, so the bacteria already in your pipes, water heater and faucets have to be killed once with bleach after it goes in. A caller in Colorado asked me exactly this: "if we still have coliform in the pipes of the house, putting in a UV ... on the other side of the pressure tank, will that be a resolution?" It will, once the pipes after it are cleaned. VIQUA's manual says to clean everything after the UV right after it's installed, and again any time the UV has been shut off or lost power.

1. Shut off the water at the main

   Close the main valve, open a faucet after the UV to let the pressure off, then close that faucet. Leave the UV plugged in the whole time.

2. Let the pressure out of the filter canister

   Press the pressure-relief button on top of the sediment filter canister (the housing the cartridge sits in) ahead of the UV. On a Big Blue it's the red button.

   

3. Take out the sediment cartridge

   Unscrew the canister with its wrench and set the cartridge aside. The canister is full of water and heavy, so have a bucket ready.

   

4. Pour 2 cups of bleach into the canister

   Household bleach (VIQUA's manual assumes the 5.25% kind), straight into the empty canister, then screw it back on.

5. Open each faucet until you smell bleach

   Turn the water back on. Open each faucet after the UV, cold and then hot, until you smell bleach, and close it.

6. Let the bleach sit 30 minutes

   Don't use any water while it sits.

7. Flush until the bleach smell is gone

   Put the cartridge back in. Run every faucet and shower for at least 5 minutes, until you can't smell bleach, and flush every toilet.

Then retest. Wait until the chlorine is completely gone before you send a sample; after a well shock, CDC's wait is 7 to 10 days.

Frequently asked questions