Both bacteria and viruses are microorganisms regulated by EPA’s Maximum Contaminant Levels (MCLs) criteria. Viruses are the smallest form of microorganisms capable of causing disease, particularly those of a fecal origin infectious to humans by waterborne transmission; bacteria are typically single-celled microorganisms that can also cause health problems in humans, animals or plants, despite many form’s ability to aid in water pollution control.

Common waterborne bacteria and viruses and their health concerns

Various types of bacteria/viruses are categorized as pathogens, disease-causing organisms that can be found in pretreated and/or inadequately treated water. Here is a list of EPA regulated bacteria/viruses in drinking water, and their health risks:

  • Legionella, a bacteria found naturally in the environment — typically in water, thrives in warm waters; this bacteria in water is a health risk if aerosolized (e.g., in a shower or air conditioning system) and inhaled, resulting in a type of pneumonia known as Legionnaires disease.
  •  Enteroviruses are small viruses, such as polioviruses, echoviruses and coxsackieviruses, living in the intestines of infected humans or animals; in addition to the three different polioviruses are 62-nonpolio enteroviruses that can cause disease in humans ranging from gastroenteritis to meningitis.

Bacteria and viruses can also be listed as “indicators,” which at a level outside of identified limits, may reflect “a problem in the treatment process or in the integrity of distribution system,” according to the EPA. Here is a list of EPA regulated viral/bacterial indicators and their potential problems:

  • Turbidity refers to the cloudiness of water and, although not a bacterium/virus, can hinder disinfection, providing an environment for microbial growth and can indicate the presence of bacteria/viruses as well as other disease-causing organisms that can produce symptoms such as nausea, diarrhea, cramps and headaches.
  • Coliforms are bacteria naturally present in the environment and used as indicators that other possibly harmful bacteria may be present (a warning sign is if coliforms are found in more samples than allowed).
  • Fecal indicators, Enterococci or coliphage, are microbes that can indicate human or animal wastes in water; they can cause short-term health effects, including: Cramps, nausea, diarrhea, headaches and more, and may pose a greater risk for people with severely weak immune systems, elderly, young children and infants (Enterococci are bacterial indicators of fecal contamination and coliphage are viruses that infect E. coli).
  • E. coli and fecal coliform are bacteria whose presence can indicate water contaminated by human or animal wastes , causing short-term health effects, including: Cramps, nausea, diarrhea, headaches and more; they may also pose a greater risk for people with severely weak immune systems, elderly, young children and infants.