The presence of coliform bacteria in a private well signals that the water system’s integrity may be compromised, indicating a potential pathway for contamination. While coliforms are often harmless, their detection warns that disease-causing organisms, known as pathogens, could also be entering the water supply. Testing for these indicator organisms is a standard, cost-effective way to assess the sanitary condition of a well, since testing for every possible pathogen is impractical and expensive. A positive test result does not automatically mean the water is unsafe to drink, but it necessitates swift action to identify the source of the problem and prevent the entry of more dangerous microbes.
Defining Coliform Bacteria
Coliforms are a large group of bacteria found ubiquitously in the environment, including in soil, vegetation, and the digestive tracts of warm-blooded animals. These organisms are rod-shaped, Gram-negative, and ferment lactose sugar, a characteristic used in laboratory testing. The majority of these bacteria do not cause serious illness in humans, but their widespread presence makes them excellent indicator organisms for water quality screening.
Water quality testing relies on coliforms because they are easier and more cost-effective to detect than the numerous pathogens that might be present. If coliforms enter the well, it suggests a breach in the physical barriers designed to keep surface contaminants out of the groundwater. Coliforms tend to survive in water environments for a similar or longer duration than many dangerous pathogens, making their absence a good indication of microbiologically safe water.
The Critical Distinction: Total vs. Fecal Coliforms
The initial test for well water safety is typically for Total Coliforms, a broad group encompassing bacteria from various sources, including soil and surface water runoff. The presence of Total Coliforms primarily signals a problem with the well’s physical structure, such as a faulty seal or casing, allowing environmental bacteria to infiltrate. This finding confirms a breach exists, increasing the risk of future contamination, though it is not usually an immediate health threat.
A more serious finding is the presence of Fecal Coliforms, a subgroup originating specifically from the intestines and feces of warm-blooded animals. The detection of these bacteria is a direct indication of recent fecal contamination, which significantly raises the risk of waterborne illness. The most important species within this group is Escherichia coli (E. coli), and its confirmed presence is the most critical finding in water testing.
E. coli is considered the best indicator of fecal pollution because its presence almost always signals direct contamination from animal or human waste. While many strains of E. coli are harmless, its detection means that disease-causing organisms, such as bacteria, viruses, or protozoa, are likely to be present. A positive E. coli result necessitates immediate action, such as boiling all water intended for consumption, until the well is disinfected and retested.
Identifying the Source of Contamination
Coliforms enter a private well through physical pathways that compromise the well’s isolation from surface contaminants. Common causes include a faulty or unsecured well cap, which allows insects, small animals, or contaminated surface water to enter the casing. Cracks in the well casing or a deteriorated annular seal (the cement grout barrier) can also create a direct conduit for bacteria.
The well’s location relative to potential pollution sources is another significant factor. Wells situated too close to septic systems, drain fields, or concentrated animal feeding operations are at high risk, especially if the ground is porous or the water table is shallow. Heavy rainfall or flooding can overwhelm the ground’s natural filtration capacity, causing surface runoff carrying animal waste to seep into the well. Contamination can also be introduced temporarily during maintenance or repairs if proper disinfection procedures are not followed.
Remediation and Prevention Strategies
Upon receiving a positive coliform test, the immediate priority is to stop using the water for drinking, cooking, or brushing teeth. Consumers should switch to bottled water or boil their tap water for at least one full minute to kill any potentially harmful microbes. The standard immediate treatment is shock chlorination, which involves introducing a high concentration of chlorine, typically unscented household bleach, into the entire well system.
This process requires circulating the chlorine solution throughout the well, pump, and household plumbing, allowing it to sit for several hours to neutralize the bacteria. After disinfection, the system must be thoroughly flushed to remove the concentrated chlorine before the water is retested. It is recommended to seek guidance from a licensed well contractor for complex shock chlorination to ensure the procedure is safe and effective.
For long-term protection, the physical source of the contamination must be identified and eliminated. This often involves repairing the wellhead, sealing casing cracks, or diverting surface water away from the well. Ongoing prevention relies on regular maintenance and testing to ensure the well’s structural integrity is maintained.
Well owners should have their water tested for coliforms at least once per year, and immediately after any well component repair or maintenance. Prevention also requires ensuring the well cap is watertight and the area surrounding the wellhead is kept clean. Additionally, maintaining proper distance separation between the well and a septic system (typically 50 to 100 feet) is a fundamental long-term strategy.