What to Do If Your Well Water Tests Positive for Coliform

What are coliform bacteria and why are they used as indicators of water quality?

Coliform bacteria are a broad group of microorganisms found in soil, surface water, and the digestive tracts of warm-blooded animals. Because they are easier to detect than more dangerous pathogens, they serve as indicator organisms, with total coliforms signaling that the environment may allow fecal contamination to reach your tap.

How can I determine if the coliform present in my water is E. coli?

You must request a specific "fecal coliform" or "E. coli" presence/absence test from your laboratory, as standard coliform tests do not distinguish between environmental bacteria and those originating from human or animal waste.

1. Contact a state-certified lab to specifically request an E. coli-specific analysis, often performed using a membrane filtration or enzyme substrate method.
2. Make sure your sample bottle contains sodium thiosulfate to neutralize any residual chlorine that could kill the bacteria before they reach the lab.
3. Keep the sample chilled at 1 to 10 degrees Celsius during transport to prevent bacterial growth.
4. Deliver the sample within 24 to 30 hours of collection to meet regulatory holding time requirements.

What are the potential health risks associated with consuming water contaminated with coliform bacteria?

While many coliforms are harmless, their presence indicates that disease-causing pathogens may have entered your supply, leading to significant gastrointestinal distress.

• Diarrhea: This common symptom often begins within 24 to 48 hours of ingesting contaminated water and can lead to rapid dehydration.
• Abdominal cramps: Sharp, persistent pain in the gut is a frequent indicator of infection from pathogens like Giardia or Cryptosporidium.
• Fever: Elevated body temperature often accompanies bacterial infections, signaling that your immune system is fighting an active pathogen load.
• Vomiting: Severe nausea and forceful expulsion of stomach contents occur frequently when high concentrations of fecal-derived bacteria are ingested.

How should I properly collect a water sample for laboratory testing?

Collect the sample from a cold-water tap, ideally one without an aerator or screen, after running the water for 5 minutes to clear the service line. Sterilize the faucet mouth with a flame or alcohol wipe, and avoid touching the inside of the bottle or cap to prevent cross-contamination from your skin. A lot of people assume that running the water for a long time improves accuracy, but excessive flushing can actually pull sediment from the well that isn't representative of the water you usually drink.

What are the most effective methods for disinfecting a private well after a positive test result?

Shock chlorination remains the primary method for sanitizing a well, typically involving the introduction of a high-concentration chlorine solution—often 200 parts per million—into the well casing. This requires calculating the volume of standing water in the well to achieve the necessary concentration, followed by circulating the water through all household plumbing fixtures until a strong chlorine odor is detected at every tap.

The system must then remain undisturbed for at least 12 to 24 hours to allow the disinfectant to penetrate biofilms on the well screen and pump components. One nuance is that if your well has an extremely high flow rate or is located in a fractured bedrock aquifer, the chlorine may dilute or wash away too quickly, necessitating a professional-grade continuous chlorination system instead of a one-time shock.

How can I identify potential sources of contamination in my well system?

Inspect the area within 50 feet of your wellhead for potential hazards like septic systems, animal waste, or chemical storage. A properly constructed well should have a casing that extends at least 12 inches above the finished ground level to prevent surface water from entering the system during heavy rain.

What steps should I take to ensure my water is safe to drink while waiting for re-test results?

You should rely exclusively on alternative sources of water until the lab provides a negative result for both total coliform and E. coli.

• Bottled water: Use this for all drinking, cooking, and ice-making needs to avoid any risk of ingesting harmful pathogens.
• Boiled water: If you must use tap water, bring it to a rolling boil for at least 1 minute to kill most biological contaminants.
• Disposable plates: Use these to avoid washing dishes in contaminated water, which could transfer bacteria to your clean utensils or cookware.
• Hand sanitizer: Keep an alcohol-based sanitizer near the sink to use after washing your hands with the potentially tainted well water.

How frequently should I test my well water to ensure ongoing safety?

At a minimum, private well owners should test their water for coliform bacteria and nitrates once every 12 months. This annual cadence helps establish a baseline for your water quality and can reveal gradual changes in the surrounding groundwater, such as those caused by shifts in seasonal rainfall or nearby land-use changes.

However, you should increase this frequency if you notice any changes in taste, odor, or clarity, or if you have performed maintenance on the pump or plumbing system. One exception is when a flood or heavy storm event occurs, as these incidents can physically compromise the well seal or force surface runoff into the aquifer; in such cases, you should test immediately regardless of when your last annual check occurred.