Total Coliform Bacteria in Private Drinking Water Wells

Total coliform bacteria occur naturally in the environment. If a water test indicates the presence of total coliform bacteria, the next step is to attempt to identify and eliminate the pathway of contamination into your well. Boiling, chlorination, ultraviolet light, microfiltration, and distillation are treatment options for removing the bacteria. Bottled water is an alternative for drinking and cooking until the problem can be corrected.

The Maximum Contaminant Level (MCL) for total coliform bacteria in drinking water is zero colonies per 100 milliliters of water. The total coliform test is the basic yardstick for determining the biological quality in a water supply. The test is inexpensive and is an easy way to check the bacteriological safety of your well water supply. The organisms in the total coliform group are called indicator organisms. The presence of coliform bacteria in drinking water indicates that a pathway for disease producing (pathogenic) organisms exists. There may or may not be pathogenic organisms in the drinking water; however, the presence of total coliform triggers the need to inspect and eliminate any deficiencies to your well which can be a potential pathway for total coliform to enter your well.

Potential Health Effects

Health symptoms may include diarrhea, cramps, nausea, possible jaundice, and associated headaches and fatigue. These symptoms may be caused by several other factors not associated with bacteria in drinking water; therefore, if you are experiencing any of them you should test your well for the presence of total coliform bacteria. Water contaminated with bacteria should not be used for drinking or cooking unless you bring it to a rolling boil for a minimum of one minute or the water is disinfected by other means. Please refer to our Disinfection Procedure for Private Wells for additional information.

Indications of Bacteria in Drinking Water

Bacterial contamination cannot be detected by sight, smell, or taste. The only way to know if a water supply contains coliform bacteria is to have it tested. In addition, there are sulfur-reducing bacteria that can be present in deep wells. If present in high concentrations, these bacteria can cause the well water to have a rotten egg smell. If iron bacteria are present, they can give a musty odor to the water and give the water a brownish tint. Sulfur and iron bacteria are not the same as total coliform bacteria so they must be tested separately.

Testing for Bacteria in Private Drinking Water Wells

The primary test to determine the presence of bacteria is the total coliform test. To determine if bacteria are present, arrange to test your drinking water at a state certified laboratory. Follow the laboratory instructions carefully to avoid contamination of the sample. Before collecting the sample, flush the pressure tank, bypass all treatment, and remove the faucet aerator. Run the cold water for several minutes and then collect your sample. Test your well water for bacteria under the following conditions:

At least annually (preferably semi-annually, spring/fall).
When a new well is constructed.
When an existing well is returned to service. If the home has been unoccupied for a while, flush the water storage tank and allow the water to run for about 20 minutes with the faucet open fully before collecting the sample.
Anytime a component of the water system is opened for repair. This includes the well, pump, pressure tank, piping, and any other components that your drinking water comes into contact with.
Whenever flood water or surface runoff inundates the well.
Whenever you suspect bacterial contamination, as might be indicated by continuing illness in the house.
When a state certified laboratory test indicates nitrate concentrations above 10 milligrams per liter or when test results show any other nitrogen components increase and human or livestock waste is the suspected cause.

If Water Tests Indicate the Presence of Coliform Bacteria

If a water test indicates the presence of coliform bacteria, you should not drink the water or use it for cooking, brushing teeth, etc. The next step is to attempt to identify and eliminate the source of contamination. If you are unable to locate and eliminate the bacteria source and cannot afford a new well, you may need a long-term treatment method. Overall, long-term treatment methods may result in being the most expensive alternative due to continuous operation and maintenance costs.

As you attempt to find the source of contamination, evaluate both the well location and well construction. Check the entire water distribution system for potential problem areas, including a garden hose without proper backflow prevention.

A well that is downhill from a source of bacterial contamination runs a greater risk of contamination than a well on the uphill side of the pollution source. Good well location requires maintaining minimum separation distances from sources of potential contamination while using the natural protection provided by soil filtration. Contact a well registered driller or licensed pump installer for all well maintenance or repairs.

Sources of Bacteria in Drinking Water

Most coliforms are harmless bacteria that are found in large numbers in the intestines and feces of warm-blooded animals and occur naturally in soil and vegetation. While most coliform bacteria are not harmful, their presence indicates the possible existence of pathogens in the water supply. Coliform bacteria should not be present in a properly constructed well. When looking for potential pathways for coliform intrusion, the following sources should be investigated:

Human Waste associated with malfunctioning septic systems and leaking sewer pipes have been identified as a potential source of bacterial contamination to a drinking water well. A septic system is designed to physically trap bacteria in the receiving soils of the leaching field. The bacteria will die in unsaturated soil conditions. Maintaining a minimum horizontal separation distance of 75 feet between your well and the septic system will provide for better protection of your well from bacteriological contamination.
Animal waste is a common source of bacteria in water. These sources of bacterial contamination include runoff from feedlots, pastures, dog or chicken runs, and other land areas containing other animal wastes. Bacteria from these sources can enter wells that are open at the land surface, that lack water-tight casings or caps that are shallow or have a well casing that is not adequately sealed in the bedrock.
Insects, rodents or other animals entering the well are also potential sources of contamination. Dug wells are more likely to have large access openings and casings that may not be properly sealed. This makes it easy for insects, rodents, or other animals to enter the well.
Inundation or infiltration of the well by floodwaters and surface water runoff can result in high levels of bacterial contamination to the water supply. Even small depressions around the wellhead that fill with surface runoff provide an excellent breeding ground for bacteria. Bacteria can easily enter your water supply when the well is shallow and/or the well casing is not properly sealed and watertight.
Older wells and water sources such as dug wells, spring-fed systems and cistern-type systems are very vulnerable to total coliform bacteria and other pathogenic contaminants. Any systems with well casings or well caps that are not watertight or lack a grout seal in the annular space are vulnerable. This is particularly true if the well is located where surface runoff can accumulate and enter the well. Well construction has improved to the point where bacterial contamination due to poor well construction is not common in newer wells.

Corrective Action

The immediate corrective action is to disinfect the well with a chlorine bleach solution; however, disinfection may only be a temporary remedy. For more information, please review our Disinfection Procedure for Private Wells.

The most important consideration is to find and eliminate the source of the contamination. Most bacterial problems are caused by improper construction or were introduced during well maintenance or repair. Some examples of corrective actions that can be made include:

Replacing an older stye well cap with one that has watertight gasket seals.
Replacing a cracked or broken dug well cover with one that fits tight over the well tiles.
Repairing any malfunctioning septic systems.
Diverting surface water away from the well.
Repairing or deepening the existing well.
Drilling another well to obtain a safe supply from a deeper level of groundwater.
Removing livestock or pets from the area around the well to prevent feces from accumulating on the ground.

All efforts should be made to identify and eliminate the source of bacteria. If the problem is due to a failing septic system, improper well maintenance, or proximity of the well to areas where feces from animals can accumulate; consider the costs of improving these situations over the long term versus long-term water treatment. If you cannot identify and correct the bacteria source, then there are home water treatment options available to you. These include ultraviolet radiation, distillation, ozonation, and microfiltration. For more information on these treatment options, please see the following:

Regardless of the quality of the equipment purchased, it will not operate unless maintained in accordance with the manufacturer’s recommendations. Keep a logbook to record equipment maintenance and repairs. Maintaining equipment may include periodic cleaning and the replacement of some components. Also consider any special installation requirements that may add to the equipment costs. For more information about treatment systems, please refer to: Questions to Ask When Purchasing Home Water Treatment Equipment.

Protection of Private Drinking Water Supplies

You can protect your private well by paying careful attention to what you do in and around your home as well as your neighbor’s activities near your well. Regular testing and adopting practices to prevent contamination can help ensure that your well supplies you and your family with good quality drinking water. For more information on well protection see Private Wells - Types & Construction.