Bacteria in Drinking Water
Barbara Liukkonen, Water Resources Education Coordinator, author and contact
Craig Hassel, Extension Specialist, Food and Nutrition, contact
Not all bacteria that exist in water supplies pose a health hazard to humans. Coliform bacteria include 15 species and most do not cause disease. However, a limited number can cause gastro-enteritis, most notably enteropathogenic E. Coli (E.E.C.). Other species can combine with fecal streptococcus to cause infection.
Large numbers of coliform bacteria live in the intestinal tracts of warm and cold blooded animals and are easy to identify during routine water testing. Therefore, they are frequently used as indicators that a water supply may be contaminated from human or animal wastes.
Coliform bacteria are carried in feces and waste water and may be found in groundwater or surface water contaminated by seepage from septic systems or feedlots. If coliform bacteria show up in a water sample, it is possible that disease-causing bacteria, viruses, and parasites from improperly treated waste water are also present. The disease-causing agents that accompany coliform bacteria are a health risk. Generally, the health risk is related to transmission of contagious diseases, such as typhoid fever, cholera, hepatitis, dysentery, diarrhea, or giardiasis.
There are several steps you can take to ensure the safety of your water supply. The first is to test for coliform bacteria. If coliform is found in a water supply, they may indicate human waste, animal waste, surface water, or other sources of contamination. The second step is to identify and correct the problem, such as a failing septic system, or one that wasn't constructed or maintained properly. The third step is to disinfect the well. The fourth step, following corrective action and disinfection, is to resample the well water to insure that the problem has been completely solved. A fifth step is additional follow-up tests after six months and one year.
Well water samples should be analyzed promptly (within at least 24 hours). Routine analysis is generally for Total Coliform Bacteria, which includes all relatives of the coliform group and serves as an indicator of contamination by waste water. Analysis of fecal coliform bacteria may be used to indicate whether the contamination is from human or animal waste. Total bacteria analysis measures the presence of all (any) bacteria, including harmful and nonharmful types.
Water testing in your area may be provided through your county health dept, local hospital, Minnesota Extension Service county office, private laboratories, or water treatment companies. Testing is generally simple and inexpensive.
The primary drinking water standard established by the U.S. Environmental Protection Agency (USEPA) standard for coliform bacteria in public water supplies is 0 colonies in 100 milliliters (m1) of water. The Minnesota Department of Health has also set the Recommended Allowable Limit (RAL) for coliform bacteria in private water supplies at 0 colonies in 100 ml of water. Thus the appearance of any colonies of bacteria indicates some form of contamination.
Shallow wells are particularly susceptible to bacterial contamination. It is, therefore, important that these wells be properly constructed, cased, and maintained and that septic systems be built to code and pumped out regularly.
Water from a newly constructed well should be tested before use. Twenty-five percent of samples from new wells are coliform positive. The contamination is not from sewage, but from the introduction of coliform during drilling, pump installation, plumbing, or sampling.
During times of drought or lowered water table levels, new drainage pathways may be established for groundwater seepage or recharge. When a well has been pumped "dry," even if it recharges rapidly, new surface or groundwater connections may be established that provide opportunities for the introduction of bacteria. Bacteria may also enter your water supply when the well or plumbing system is repaired.
The well and household plumbing should be disinfected whenever there is repair or replacement of pumps, cisterns, hot water heater plumbing, or plumbing fixtures. Shock disinfection is a simple process that will eliminate all forms of bacteria or other living organisms in the water supply, provided sufficient chlorine is added. If bacteria continue entering a defective well, disinfection becomes a temporary measure and a permanent water treatment system may be necessary.
Other non-disease causing bacteria may inhabit a private water supply. These include the iron or sulfur reducing bacteria that cause water to smell or taste like "rotten eggs." These bacteria ordinarily live in the soil or aquifers, but they may multiply rapidly once they are introduced to a well or household water system, particularly when the water is high in iron. This may occur when there is a direct surface water connection to your groundwater supply or when you have had maintenance on some portion of your plumbing system.
Once iron or sulfur reducing bacteria begin to multiply and gain a strong foothold in your water supply, they may contaminate the entire aquifer. At that point, eliminating them may be very difficult. In some cases, repeated disinfection is required to eliminate or reduce bacteria to tolerable levels.
The Minnesota Department of Health recommends periodic testing of private water supplies for coliform bacteria. For information on water testing services, water treatment devices and bacteria in your drinking water, contact your county or city health departments, community health service agencies, medical care providers, Minnesota Department of Health district offices, or your Minnesota Extension Service county office.
For additional information on bacteria and drinking water, contact:
Barbara Liukkonen
Water Resources Education Coordinator
Water Resources Center
173 McNeal Hall
1985 Buford Ave.
Saint Paul, MN 55108
Phone: (612) 625-9256
Craig Hassel
University of Minnesota Extension
225 Food Science and Nutrition Bldg.
University of Minnesota
1334 Eckles Ave.,
St. Paul, MN 55108
Phone: (612) 624-7288
Minnesota Department of Health
Building:
Well Management Section
Environmental Health Division
Minnesota Department of Health
625 North Robert Street
St. Paul, MN 55155-2538
Mailing:
Well Management Section
Environmental Health Division
Minnesota Department of Health
P.O. Box 64975
St. Paul, MN 55164-0975
Phone: (651) 201-4600 |
