lColiform Bacteria

Are harmless to humans, and are only used as an indicator bacterium.  The idea is that is Coliform can get into a well, so can the harmful ones, such as E-coli.

Coliform can live anywhere there is organic material, where as the E-coli can only live where there is human or animal waste.  Coliform Bacteria can be found anyplace there is moisture and nay insects.  Over 90% of all Coliform lives within the top centimeter of the ground.

Low counts of Coliform in a well or water distribution system are probably harmless.  Some kinds of Coliform can stay alive in a water system even without an outside food supply.  If the system is disinfected, the counts will generally go to zero.  If the low counts persist, the well should be checked out.

If counts are high or change radically from one test to another then surface water could be entering the well.  It may be through a failing seal at the bottom of the casing, or insects entering the well through a faulty well cap.

For details on how to disinfect your well, go to our Well Disinfection page above.


E-coli belong to the Coliform group of bacteria's.  When E-coli is present, raw sewage is also present. 

Labs can easily identify E-Coli, but it is not so easy to figure out what strain it is.  About 1 percent of the wells on PEI test positive for E-Coli.  There are about 110 strains of these bacteria, and of those about a dozen are harmful.  Close to 100% of the E-Coli problems on PEI are caused by leaky septic tanks.  Contamination from farm animals is rare.

E-Coli comes from the intestines of warm blooded animals.  The biggest producers on PEI are Humans, Cattle, and Pigs.  In a human, 20 Billion E-Coli are produced and discarded in Feces every day.  The total number of all bacteria in the large intestines of a human is about 100 Trillion.  It is the job of many of these to kill intruders.  With few exceptions, E-Coli indicates that surface water is entering the well.

Coliform In A New Water System

When the new pump is installed, all it takes is an insect, or a blade of grass to get into the well via the pump, pipe, or electrical wire.  Any plumbing such as pipes, water tanks, etc, could have been a temporary home for insects or spiders.  If hard shelled bugs get in the system, it can take months of disinfecting to get a Coliform count to zero.

Sometimes the vermin proof well caps are installed wrong or get damaged.  If so bugs can enter through the conduit where the electrical wires enter the well cap. 

When the screen on the tap is not taken off when taking a water sample.

For the most part, the well gets the blame for unsanitary piping in the house.

Debate Over Coliform Testing

There has always been a debate on whether to use Coliform as an indicator for contamination.  In parts of Europe, E-Coli is used as an indicator for contamination, not Coliform.

This quote is from one of the largest laboratories in the U.S:

"Coliform counts of less than 100 ppm per 100 ml sample are believed to be environmental bacteria thought of as regularly being housed in the well and not being added to by outside contamination."  Assuming that the well has been investigated and no source of outside contamination was present.  Johnson Screens - 2003.

A recent University study found that it is possible for a well to get some Coliform in it during and up to 3 hours after a heavy rain.  If the well vent sucks in air at this time, the high humidity could bring in some Coliform form the surrounding vegetation.

When our water test report says Background 25 for example, that means that there are 25 bacteria found that the lab cannot identify.  Other than to say that they are not disease carriers and are not harmful.