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What Causes Bacteria in Drinking Water?

Dutch scientist Antony van Leeuwenhoek first described bacteria in 1673, which led to the development of the germ theory of disease and of sanitation practices for the public drinking supply system. Bacteria exist everywhere: in the air, in the guts of mammals and humans, in the soil and in the water. Some bacteria are helpful, as flora in the intestines or as antibiotics. Other bacteria are harmful, such as coliform in water that causes sickness.

  1. Fecal Matter

    • Coliform bacteria in various forms are found in the intestinal tracts of mammals and humans and are therefore spread through fecal matter. Coliform enters the drinking water system through stormwater or agriculture runoff, flooding and contamination from seeping underground sewage pipes. While most coliform bacteria do not cause disease, some strains do, such as the Escherichia coli (E. coli). Water contaminated by E. coli is a serious health issue, and therefore municipal water facilities routinely test for its presence in the public water supply.

    Poor or Malfunctioning Plumbing

    • Poorly installed or maintained equipment or a malfunctioning well system may cause bacterial contamination of drinking water. In new construction, a well must be back-filled around the well casing and all pipes and holes sealed from underground water seepage into the well. Older wells or land that has experienced severe flooding may cause the underground well system to shift or spring leaks. Pipes that have shifted may backflow, channeling bacteria-laden water into the drinking supply.

    Biofilm

    • Biofilm is the bacterial sludge that coats the interior pipes of a drinking water system. Despite the seemingly smooth material, a water pipe has very tiny ridges and burrs where sediment, mineral deposits and small organic matter collect. Large deposits of coliform biofilm may grow and eventually break off from the colony into the flow of water through the pipes. The bacteriostatic properties of copper pipes, a common water supply material, are known to reduce the formation of biofilm. With the rise of alternative potable plumbing materials, such as cross-linked polyethylene (PEX) pipes, polyethylene vinyl plastic (PVC) and the galvanized iron pipes existent in many older homes, biofilm may be more prone to contaminating the drinking water supply of a single building or building unit.

    Lacking or Malfunctioning Water Filtration

    • Underground, bacteria naturally bubble toward the surface as the groundwater moves through the soil. A deep dug well with inadequate or nonexistent filtration will collect bacteria traveling through the soil or pool bacteria within the water itself. While the homeowner can certainly install a water filtration system at the point of water outflow above ground, the New Hampshire Department of Environmental Services warns that contamination could possibly overwhelm the filtration system at times. Malfunctioning equipment or trauma to the system from, for example, repairs or nearby construction, may fracture the underground equipment and introduce bacteria from the surrounding environment.

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