Coliforms & E. coli

The source of bacterial contamination

Under ideal conditions, deep groundwater is naturally purified. As surface water percolates down through layers of soil, sand, and rock, bacteria and pathogens are naturally filtered out. When coliforms or E. coli are detected in a well, it means this natural filtration system has failed or been bypassed.

• Total coliforms: This is a broad family of bacteria found naturally in soil, plants, and surface water. Their presence in a well doesn't always mean the water is dangerously contaminated with feces, but it acts as an "indicator." It means surface water is getting into the well, which means worse pathogens could get in too.
• E. coli (Escherichia coli): This is a specific subgroup of coliform bacteria found exclusively in the intestines and feces of warm-blooded animals (like us). If E. coli is in the groundwater, it is absolute proof of recent fecal contamination.

How does fecal matter reach the aquifer? It almost always requires a structural breach or a localized environmental overload:

• Failing septic systems: If a home's septic leach field is located too close or upstream to the wellhead, or if the septic tank is cracked and leaking, untreated human wastewater can seep directly into the groundwater.
• Agricultural runoff: Heavy rains can wash livestock manure from nearby farms and pastures into the soil, overwhelming the natural filtration.
• Cracked well casings: The steel or PVC casing that lines a well is supposed to keep shallow surface water out. If this casing cracks due to age, or if the sanitary seal at the top of the well fails, contaminated rainwater or snowmelt can pour directly down the shaft into the drinking water supply.

Why avoid fecal contamination (in case you've been living in a cave)

• Severe health risks: The primary and most critical effect. Consuming water contaminated with E. coli can cause severe gastrointestinal illness, including stomach cramps, diarrhea (often bloody), and vomiting. Certain strains, like E. coli O157:H7, can cause life-threatening kidney complications, especially in children, the elderly, and immuno-compromised individuals.
• Biofilm formation: Coliform bacteria can contribute to the formation of a biofilm in your plumbing. While not as thick or destructive as iron bacteria slime, this biofilm can protect other harmful pathogens from chemical disinfectants and cause the water to develop a slightly swampy odor.
• Indicator organisms: The most significant effect of finding total coliforms in your plumbing is what it represents. Because coliforms are relatively easy to test for at extremely low densities, they are used as an "indicator organism." If they made it into your pipes, it means the plumbing system is highly vulnerable to much more dangerous, harder-to-detect pathogens, including viruses (like Hepatitis A) and parasites (like Giardia or Cryptosporidium).

Treatment

For domestic treatment of microbial contamination, the most effective method with minimum treatment for water pumped directly from wells is ultraviolet (UV) sterilization. A UV filter sized appropriately to the household's maximum flow is a simple and effective protection for your water, but the system must be fitted with a sediment filter in order to be effective. Sediment will protect adhering bacteria in biofilms and block light directly. Also, water high in color, iron and/or manganese or in hardness would require treatment prior to entering a UV filter, since they all may effectively block the UV light and therefore the effectiveness of the system. Colored compounds may directly absorb the UV light, while metals and hardness can block light by forming precipitates on the bulb's sleeve.

If a storage tank is in use, ozone (O₃) can be used as an effective disinfectant. Ozone can be generated on-site with relatively inexpensive corona-discharge-type O₃ generators and purged through the water with a small aquarium air pump to keep these tanks sanitary and free from microbial growth.