My well water tested positive for coliform bacteria! What now?
First of all, don’t panic! Yes, a positive total coliform test can mean your water is contaminated with e-coli, but not always. So let’s look at what it all really means.
What are coliform?
Coliforms are a family of bacteria that occur naturally in soil and decaying vegetation as well as in the intestines of warm-blooded animals, including humans. The presence of coliforms on a water test indicates the potential presence of disease-causing microorganisms (bacteria, viruses, and protozoan cysts) in water – or, at least, that a pathway exists for those bacteria to enter the water. That’s why they’re often referred to as “indicator organisms”.
Are coliform harmful or dangerous?
Many coliforms are completely harmless. Fecal coliforms, however, like E.coli, can make people sick with symptoms that include diarrhea, cramps, nausea, and headaches, and can even lead to kidney failure. That’s why a positive coliform test should be taken seriously – especially if infants, young children, the elderly, or people with compromised immune systems live or frequently visit the household.
What does a positive coliform test mean?
When a water test indicates a high “Total Coliform” count, the water may or may not contain illness-causing strains such as E.coli. But, when present, coliform are a strong indicator that your water source has already been or can easily become contaminated with fecal matter, and you should disinfect your water. As the source of coliforms is most often an environment external to your water source, a positive test indicates the security of the water source might be compromised. A positive test for coliforms should always be followed by – or completed in conjunction with – a more specific E.coli test. Generally speaking, if your water tests positive for total coliforms but negative for E.coli, surface water has infiltrated the well. If your water tests positive for total coliforms and positive for E.coli, there’s a fecal contamination source, which could be a leaking septic system or agricultural runoff containing animal waste. In any instance, the risks in both scenarios are real in that pathogenic (disease causing) organisms can be present. It is important to understand what is used as an indicator and what is commonly the cause of water borne illness are different microorganisms. For this reason, indicator tests should be done frequently and results taken very seriously.
Total coliforms alone aren’t necessarily worth panicking over. But if there are coliform, other things may come along with it, like enteric viruses. Relying solely on indicator organisms underestimates a true pathogen being present by about 50%.
Potential causes of a positive coliform test
There are several common sources of contamination:
- Heavy rain or flooding
- Leaking septic systems.
- Agricultural runoff that contains manure, either from livestock operations or manure that has been spread on fields as fertilizer.
Extreme weather events can overwhelm even properly constructed, newer wells and can introduce surface contaminants into the aquifer below. If your well is older, there are even more potential avenues for surface contamination to enter your drinking water.
Remember that many wells may draw water from the same aquifer. This means if your neighbors don’t maintain their wells properly, your water can become contaminated. Certain pathogens, like viruses, can travel thousands of meters.
Also note that you should be testing your water at least once a year – some experts recommend three times a year or more.
Coliform drinking water standards – how much coliform is safe?
Water test results can be confusing, but they don’t have to be difficult to interpret. Your target – and the target set by government health agencies – is always a Total Coliform count of 0 or Not Detected. Presentation of results may vary by lab or locale, but the standard explanation is as follows:
|0 or ND (not detected)||Your water is safe for drinking.|
|1 or higher*||Your water is not safe for drinking unless you boil it.|
|O/G||Your water is not safe to drink unless you boil it. Sometimes, your test results will say “O/G” or “overgrown” instead of listing the number of total coliforms. This means there are so many other types of bacteria in your water sample, the lab technicians couldn’t see whether there were any coliform bacteria.|
|*If you see “est.” or “estimate” next to your test results, it means there were coliform bacteria in your water. However, because there were so many other bacteria as well, the lab technicians couldn’t accurately count the number of coliform bacteria. Your water is not safe to drink unless you boil it.|
How can coliform bacteria be treated?
While you’re figuring out how to tackle the issue, boil your well water before you drink it or cook with it. To make sure it’s safe, bring it to a rolling boil for a full minute.
Temporary solution: Shock your well
To remove bacteria from your well, you’ll need to “shock” it with a high dose of chlorine. The amount of chlorine you need depends on the depth of your well, the pH of the water, and how much slime or biofilm is present. Keep in mind that chlorine is corrosive and should be handled with care. Leave the chlorine in the well for at least 12 hours and then purge the water. Highly chlorinated water is not safe to drink!
Better yet, call in a water treatment professional to do the job. An expert will know exactly how much chlorine is required and how to safely dispose of the chlorinated water once the shock treatment is complete.
It’s important to remember that shocking your well doesn’t offer a long-term solution for ongoing contamination issues. It’s a quick fix that needs to be paired with long-term disinfection. Sources of contamination can be very complex, so temporary solutions like shock chlorination should be relied on only if the source of contamination has already been addressed (through steps like well repairs). If the source of contamination is not known, continuous disinfection, like ultratviolet (UV) disinfection - should be applied.
Permanent solution: Install a water treatment system that includes continuous disinfection
There are a number of disinfection options. Point of use (POU) systems treat the water at a specific tap. So if you install a point of use system at your kitchen sink, for example, the water from your kitchen tap is treated, but the water coming out of your bathroom tap isn’t. It’s also important to note that pathogens in water are linked to both gastro-intestinal and respiratory – some pathogens can be inhaled through showers water. Point of entry (POE) systems treat all the water coming into the house, so you can turn on any tap knowing the water that comes out has been disinfected.
There are also different treatment technologies. While chlorination, ozonation, and ultraviolet (UV) all disinfect your water effectively, we recommend ultraviolet (UV) disinfection. UV is a highly effective, proven technology neutralizing microbes without the use of chemicals. Even chlorine-resistant microorganisms are made harmless through UV exposure. If you are on a private water supply, it is your responsibility to ensure your water’s safety. Installing a UV system on a municipal water supply provides peace of mind when aging municipal infrastructure fails.
UV water disinfection is a safe, chemical-free way to treat water. Lack of chemicals means no harmful chemical byproducts are going back into the environment, and the taste of your water is not affected in any way.
- Treats bacteria including coliforms and e.coli
- Treats very wide range of harmful viruses
- Inactivates cryptosporidium and giardia
- Absolutely no chemicals added
- No disinfection by-products
- Doesn't change taste or smell
- Just clean the sleeve and replace the lamp once per year (or 2)
- No tools maintenance
- Low operating cost