Bacterial contamination is the most common water quality problem faced by private well owners. Because there are so many different types of bacteria, the laboratory tests for only two types of “indicator” organisms; total coliform bacteria and E. coli. The results of these two tests tell us different things about the safety of your water supply.
Total coliform bacteria are a group of organisms that are occur naturally in a wide range of environments including soils, surface waters as well as manure and sewage. Their presence alone in drinking does not necessarily mean there are harmful bacteria in your water, and in the absence of E.coli, can simply be an indicator of the sanitary condition of the well or plumbing system, or that the well is vulnerable to contamination, and thus there is the potential for more harmful bacteria to also enter the well.
E. coli is a group of bacteria found in the intestines of warm blooded animals, and while not all strains of E. coli are harmful to humans, the presence of E. coli in drinking water is a clear indicator of recent faecal contamination of the water supply, usually be sewage or manure.
What are the health concerns?
The Guidelines for Canadian Drinking Water Quality recommend that drinking water contains no (0 cfu/100 mls) of total coliform or E. coli bacteria organisms. While the presence of total coliform in the absence of E. coli is not considered a serious public health threat, it can mean that a supply is vulnerable to contamination by more harmful pathogens. The presence of E. coli indicates contamination by a source of faecal material, and thus the presence of any number of harmful, infectious pathogens.
The detection of any level of E. coli, or high levels of total coliform (eg more than 10 cfu/100mls) in drinking water from a private well should result in the immediate adoption of the precautionary measures recommended under a “boil water advisory”.
In addition the water should be resampled to confirm the initial results. Depending on the results of this second sample, an investigation into the source of contamination may be initiated.
The presence of a low level (in the range of 10 cfu/100 mls) of total coliform bacteria in the absence of E. coli should be followed up by an inspection of the well and resampling of the water. If the problem persists, or if the level of bacteria in the water increases, operators should adopt the same precautions recommended above for the detection of E. coli. In either case, normal use of the water should not resume until the safety of the supply has been verified by obtaining two consecutive samples with showing no presence of bacteria.
What are the treatment options?
Many bacteria problems can be addressed by disinfection of the well and plumbing system, provided there are not fundamental problems with the well construction or nearby sources of faecal material, and it is recommended that wells be inspected and disinfected on a routine basis as part of overall maintenance of the water supply. More persistent or serious bacterial problems can be addressed by the installation of a Class A ultra-violet (U.V.) disinfection system.
We do not recommend specific brands of treatment devices; however, it is recommended that purchase devises bearing a label that indicates it has been certified to NSF Standard 55 for Ultra Violet (UV) Microbiological Water Treatment Systems.
As with the use of any drinking water treatment device, the effectiveness of treatment should be verified by sampling after installation. In addition, it is important to ensure the device is used and maintained according the manufacturer’s directions and its performance periodically confirmed by sampling.