Dealing with Coliform Bacteria in Water Wells

Published On: June 21, 2021By Categories: Drawing from the Well, Groundwater Quality

The columnist shares his series of questions to help detect the water problem.

By Gary Shawver, MGWC

One of my greatest challenges when I was in business was dealing with a water well that had coliform bacteria.

Whether it was a customer calling in regarding an existing or a new well we had drilled that had come back with a positive coliform count, it was a recurring issue that gave me the insight and ability to use a process I developed to help sort out problems.

However, realize that every well situation with coliform is different. While I developed a process, the process could vary from well to well depending on what information I was able to obtain.

So, let’s begin with a customer calling in with a well that came back with a test for coliform. Here’s a scenario I would use, and it began with a series of questions. I likened the questions to what a doctor might ask a sick patient.

Question 1:
What prompted you to take a water sample from the well?

They may answer it was a routine test they took, or often they would answer that there was some issue that caused them to take a test. These issues ranged from the water had a different odor than normal, it got dirty after a rain, or someone in the family was sick.

Most well owners don’t take a routine test yearly. If they answered other than a routine test, I would pursue further based on the answer they gave.

If they told me the water had a different odor, I would ask when it began and if it was after a heavy rain or snowmelt? That would lead me to potentially believe the well integrity was compromised. In our area, that would probably mean the casing had deteriorated to the point it had holes in it.

Question 2:

Based on the answer, if the water had a different odor, I would ask if that was the first time it happened. If it was, then I would ask how long they had lived on their property. The reason for that question was it told me how long they had been using that well, which would tell me that they had an expectation of what the water typically smelled like.

If it was a long time and it was the first time it had happened, then that told me they were attentive to the water and it would also tell me that potentially something had happened to the well integrity.

Question 3:

If they had lived on their property a long time and had this issue for the first time, I would ask how old the property was. If it was more than 60 years old, then I, again, would surmise the well integrity might be in question. The reason for the 60 years of age is wells in our area can deteriorate to the point of having holes rust through the casing.

If it was a farm property and they weren’t sure when the well was constructed, I would ask them where the well was located. The location is especially important on a farm property.


Because typically old farms had their wells initially drilled out by the livestock buildings because they often didn’t have water pressure systems and it was easier to carry the water to the house than to all the livestock. So if the well was by the outbuildings, that indicated the well was extremely old, and again, the integrity of the casing was probably compromised.

On the other hand, if the well was located by the house and it was an older farm, then that typically told me it was a second-generation well on the property. If it was located by the house, I would ask if they had any idea of when the well might have been drilled. If they were a lifelong resident of the property, they most likely knew. And again, if the well was older than 60 years, I would again suspect the casing integrity being compromised.

Some other questions on this scenario that I might ask:

Was there ever a windmill over the well?

That could be told if there were windmill stakes at four corners surrounding the well but no windmill. Again, this would date the well, and if there was a windmill, the casing was old. In our area, windmills quit being put up in the early 1940s as electrification was occurring.

Is the well in a pit?

Again, a well that’s in a well pit would point to it being an old well.

Well pits quit being used in our area in the mid-1950s as pitless adapters were being used. All these questions and their answers are clues to the well’s age and potential integrity.

So, let’s back up to the first question: What prompted them to test the water in the first place?

In among all the questions, I would invariably ask them who took the test and what was the sampling point. If the homeowner took the test, I would ask them how they took the sample. I’m not going to go into all the details here, but how one takes the sample can easily cause the sample to fail.

In addition, if the sample was taken from the kitchen sink, I would question the integrity of the water sample. Kitchen sinks are the most prone place in the home to get a coliform bacteria sample, especially in older homes.

If the sample that was taken happened to have a fecal coliform test taken also, then I would begin to surmise the well integrity is compromised as most wells with positive fecal tests can have the fecal come from one of two sources: migration of water to the well from the septic tank, or migration of water to the well from livestock runoff.

However, if the test didn’t include a fecal test, and the homeowner took the sample from the kitchen sink, I would recommend the customer take another test, but from a non-drinking water faucet as close to the pressure tank as possible.

I would also encourage them to take a fecal test. If that test came back clean, then I would encourage them to take another test in 30 days or so or sooner if something abnormal with the water occurred.

If the water test failed the second time, I would ask if I could visit the customer’s location and examine the well and see what I could observe that may be obvious.

Here’s some of the things I would look for, and again, this was if the well had a positive coliform test the second time:

  1. I would first look at the top of the well to see if it had a proper well cap or seal and if the conduit connection leading into the well cap or seal was as it should be. I often observed a lot of electrical connections poorly installed and thus not having a tight seal at the wellhead.
  2. I would take the well cap or seal off and observe the inside of the casing as far as I could see with a high-powered light. I would also listen down the well to see if I could hear water running in. Water running into the wellbore was often an indicator of a failed casing.
  3. I would also observe where the well was located in relation to the septic system and potential runoff from livestock. Also, I’d look to see if there was a depression around the well.
  4. And again, I would observe if the well was in a pit or at one time may have had a windmill over it. Sometimes, wells had been extended out of pits and I could typically see if that had occurred. Again, both situations dated the well and could be an indicator of well integrity due to age.

In some situations, I would never be able to determine where the coliform was entering the well or find a defect that would pinpoint the problem. However, I always wanted to follow these steps and ensure I was doing due diligence in ensuring the homeowner’s well was in fact needing replacement rather than just assume that because it had a failed bacteria test.

In some cases, I found that there were no defects and poor sampling was the source of the bacteria. It also gave me the opportunity to do a one-on-one with the homeowner and build a relationship with that person.

And finally, it gave me an education on dissecting coliform bacteria in wells. The public looks to water well contractors to solve their water problems, and this is one more step that we, as good contractors, need to put ourselves through to be that person.

Gary Shawver, MGWC, is vice president of Shawver Well Co. Inc. in Fredericksburg, Iowa. He has been in the water well industry for more than 40 years and is a Master Groundwater Contractor. He served on the NGWA Board of Directors. Shawver is semi-retired, having sold his business to his employees. He can be reached at


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