Is It Bad to Have Coliform in Your Water?

What specific organisms are classified as coliform bacteria?

Coliform bacteria are a broad group of gram-negative, non-spore-forming bacilli that ferment lactose to produce acid and gas at 35 to 37 degrees Celsius.

• Citrobacter species are commonly found in soil and water and are frequently identified in environmental samples.
• Enterobacter organisms are often associated with decaying vegetation and can thrive in various plumbing materials.
• Klebsiella bacteria are widely distributed in nature and can colonize both plants and the intestinal tracts of animals.
• Escherichia represents the most well-known genus, serving as the primary indicator for fecal contamination in water testing.

How do regulatory agencies determine safe levels of bacteria in drinking water?

Agencies establish safety limits using the "indicator organism" concept, which assumes that if these bacteria are absent, more dangerous pathogens are likely absent too. They monitor for the presence or absence of these organisms rather than testing for every specific virus or parasite. Many people assume that boiling water for a few seconds is enough to kill all bacteria, but you must maintain a rolling boil for at least one full minute to neutralize resistant cysts and pathogens effectively.

What distinguishes total coliforms from fecal coliforms and E. coli?

The distinction lies in the temperature at which the bacteria ferment lactose and their specific origin within the intestines of warm-blooded animals.

• Total coliforms encompass a wide variety of bacteria found in soil, water, and vegetation, making them a general indicator of environmental integrity.
• Fecal coliforms are a subset of total coliforms that specifically thrive at higher temperatures, signaling a direct link to warm-blooded animal waste.
• E. coli represents a specific species within the fecal coliform group that serves as the most accurate biological marker for recent sewage contamination.

What are the primary sources of bacterial contamination in private wells versus municipal systems?

Private wells are primarily threatened by surface runoff and structural defects, whereas municipal systems face risks from pipe corrosion or pressure loss.

Use these categories to prioritize your inspection, focusing on the wellhead for private supplies and utility alerts for municipal users.

What are the potential health risks associated with consuming water contaminated by coliforms?

Yes, consuming contaminated water can lead to gastrointestinal distress, including diarrhea, vomiting, and abdominal cramps. While many coliforms are harmless, their presence indicates that waterborne pathogens like Cryptosporidium, which can survive for months in cold water, may also be present in your supply.

What standard laboratory methods are used to detect and quantify these bacteria in water samples?

Laboratories typically use the membrane filtration method or the multiple-tube fermentation technique to detect these organisms. In membrane filtration, a measured volume of water is passed through a sterile filter, which is then placed on a selective growth medium like m-Endo agar. After incubation at 35 degrees Celsius for 24 hours, colonies showing a characteristic metallic sheen are counted as positive.

One nuance is that some bacteria, known as "stressed" or "injured" coliforms, may not grow on selective media immediately after exposure to chlorine. These organisms might require a recovery period on non-selective media before they can be accurately identified. Consequently, a negative result immediately following a disinfection procedure might provide a false sense of security if the bacteria are merely dormant.

How can homeowners effectively treat or disinfect water that has tested positive for coliform bacteria?

Yes, you can disinfect a well using a shock chlorination process, which involves circulating a high concentration of chlorine, typically 50 to 200 parts per million, throughout the entire plumbing system. You must let this solution sit in the pipes for at least 12 to 24 hours to be effective.

Why is the presence of these bacteria often used as an indicator for other pathogens?

Coliforms are used as indicators because they are more numerous and easier to detect than the specific pathogens that cause waterborne diseases. Testing for every potential virus, protozoa, or bacteria—such as Salmonella or Giardia—would be prohibitively expensive and time-consuming for regular monitoring. By using coliforms as a proxy, labs can quickly determine if the physical barrier of a water system has been breached by environmental or fecal contamination.

However, this indicator system is not perfect. Some pathogens, particularly certain viruses and protozoan oocysts, are more resistant to standard disinfection methods like chlorination than coliform bacteria are. This means that water could technically test negative for coliforms while still harboring these more resilient organisms, which is why protecting the source water remains the most effective way to prevent contamination.