Is Coliform in Well Water Dangerous?

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Key Takeaways:

  • Coliform bacteria indicate potential contamination and health risks from pathogens in well water.
  • Fecal coliform bacteria like E. coli are especially concerning as markers of fecal contamination.
  • Annual testing for coliform bacteria is recommended to monitor well water safety.
  • Disinfecting or repairing wells with coliform present reduces illness risks.
  • While not all coliforms are dangerous, their presence warrants caution about drinking untreated well water.

Well water is a vital resource for millions of households worldwide. With groundwater supplying drinking water for nearly half the U.S. population, ensuring well water safety is paramount. One critical water quality issue is the potential presence of coliform bacteria. But is coliform in well water really dangerous?

This comprehensive article will analyze the health risks and implications of coliform bacteria detection in residential well water. Key topics covered include:

  • What are coliform bacteria and how are they tested for?
  • Why do coliform results indicate potential contamination?
  • How dangerous are different types of coliform bacteria?
  • What actions should be taken if coliform is found in a well?
  • When should well owners test for coliform and other bacteria?

Gaining a thorough understanding of coliform bacteria will empower homeowners to monitor their well water quality, identify contamination issues early, and take appropriate corrective actions. Protecting well water from pathogenic bacteria is vital to safeguard the health of all household members. Read on to discover the essential facts about coliform risks in wells.

What Are Coliform Bacteria and How Are They Tested in Well Water?

Coliform bacteria are a broad class of bacteria found throughout the natural environment. They are defined as gram-negative, non-spore forming, rod-shaped bacteria that ferment lactose with gas and acid production within 48 hours at 35°C. Coliforms live in soil, surface waters, and on plants – they are not necessarily agents of disease. However, their presence in drinking water indicates potential contamination by more harmful pathogens.

There are three main subgroups of coliform bacteria tested for in well water:

  • Total coliforms – Includes a wide variety of bacteria like Klebsiella, Citrobacter, Enterobacter, and Escherichia. Total coliform count indicates overall water quality.
  • Fecal coliforms – Bacteria originating from fecal matter of humans and animals. E. coli is the primary member. Presence indicates possible sewage contamination.
  • E. coli – The predominant fecal coliform found in digestive systems of animals. Specifically indicates recent fecal contamination.

The standard test for coliform bacteria in well water is the Most Probable Number (MPN) assay. Multiple water samples are incubated with a lactose broth that promotes coliform growth. Gas production provides a positive test for total coliforms. To identify fecal coliforms, positive samples are transferred to media containing a fecal coliform indicator. E. coli can be singled out on an EC broth specific to that bacteria. Higher coliform MPN values indicate greater levels of potential contamination.

Why Do Positive Coliform Results Indicate Contamination?

Detecting coliform bacteria in well water is significant because their presence often signals contamination by more harmful microorganisms capable of causing disease. According to the Environmental Protection Agency (EPA), total coliforms themselves are not likely to cause illness. However, they indicate a pathway exists for surface or subsurface fecal matter to enter the well and water system.

Where coliform bacteria are found, there is a high probability that pathogens like Giardia, Cryptosporidium, Salmonella, or E. coli O157:H7 may also be present. These organisms can cause severe gastrointestinal illness if ingested.

Research shows 48% of waterborne disease outbreaks are linked to contaminated groundwater sources. A study by the Center for Disease Control (CDC) found that households served by wells have a 9X higher risk of contracting waterborne illness than municipal systems. Coliform bacteria are like the canary in the coal mine – they provide an early warning sign of potentially hazardous water quality.

How Dangerous Are Different Kinds of Coliform Bacteria?

Not all coliform bacteria in water pose the same level of risk. Total coliforms themselves are generally harmless. But fecal coliforms and E. coli are cause for greater concern:

  • Fecal coliforms indicate sewage or animal waste contamination. This points to probable presence of intestinal pathogens like viruses, protozoa, and disease-causing strains of E. coli.
  • E. coli is a specific fecal coliform directly linked to recent contamination by human/animal feces. According to the EPA, E. coli itself can cause illness – including diarrhea, urinary tract infections, respiratory illness, and pneumonia.
  • E. coli O157:H7 – This virulent strain produces powerful toxins and causes severe bloody diarrhea. It can lead to kidney failure and even death, especially in children and the elderly.

Positive tests for total coliforms generally prompt further testing for fecal coliforms and E. coli. The presence of any fecal coliforms or E. coli in drinking water represents an acute health hazard requiring immediate action. These results mean disease-causing microbes are likely entering the water supply via recent fecal contamination.

What Actions Should Be Taken if Coliform Bacteria Are Detected in Well Water?

If coliform bacteria are confirmed in a residential well, the following actions should be prioritized:

  • Stop drinking or cooking with the water immediately – Boiling does not remove the contamination risk. Use alternate water sources until the well water is disinfected.
  • Retest with multiple samples – Confirm initial results were not anomalous or from sampling errors. Verify if fecal coliforms/E. coli are present.
  • Inspect well infrastructure – Check well cap seal, casing joints, vent screen. Repair cracks or defects that could allow contaminants to enter.
  • Shock chlorinate the well and plumbing – High-dose chlorination kills coliform bacteria and pathogens in the well and household pipes.
  • Flush and retest the water – Pump out all disinfectant and re-sample well water to confirm bacteria removal after shocking.
  • Consider ongoing disinfection – Options like ultraviolet light or chlorination may be warranted if coliform issues persist long-term.
  • Consult experts if needed – Licensed well contractors can inspect, repair, or treat wells with complex bacterial issues.

Addressing coliform contamination quickly is critical to prevent harmful pathogens from sickening household members.

When Should Well Owners Test for Coliform and Other Bacteria?

To ensure well water safety, the EPA and health agencies recommend homeowners test for coliform bacteria in the following circumstances:

  • Annually – Test well water for total coliforms yearly as standard monitoring. Include fecal coliforms/E. coli every 3-5 years.
  • New wells – Always test new or repaired wells before drinking the water. Confirm disinfection was successful.
  • Suspicious changes – Test if water tastes/smells bad, pipes show biofilms, or sediment increases. These indicate possible bacteria growth.
  • Special events – Test after flooding, plumbing repairs, nearby construction etc. which could introduce contaminants.
  • Household illness – Test if household members suffer recurring gastric illness of unknown cause.

Annual coliform testing provides valuable data to identify increasing contamination trends before they become severe health hazards. Being vigilant and testing more frequently during unusual events or changes in water quality helps safeguard well water safety long-term.


In summary, the presence of coliform bacteria in residential well water does pose a legitimate health concern. Coliforms signal potential sewage or animal waste contamination that could allow pathogens like E. coli, Giardia, or Salmonella to enter the water supply and cause acute gastrointestinal illness.

Fecal coliforms and E. coli represent an urgent health hazard requiring immediate action, as they indicate recent fecal pollution of the well by disease-causing microbes. Prompt disinfection and infrastructure repairs are critical to resolve coliform issues. Ongoing annual testing, paired with vigilance during unusual events, provides valuable data allowing well owners to take rapid corrective action and keep their water safe.

While not all coliform bacteria are inherently dangerous, their presence in well water provides an early warning that treatment and remediation may be needed. By understanding the implications of coliform bacteria detection, homeowners can take appropriate steps to provide clean, contaminant-free water for their households. Responsible well monitoring and maintenance safeguards the health of all who rely on private groundwater resources.

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