Bacteria and viruses commonly found in drinking water

July 31, 2014

A breakdown of harmful bacteria and viruses and what techniques are used to treat them.

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.

Popular bacteria/virus treatment technology

The amount and type of water treatment can vary depending on the type of bacteria/viruses present. Some of the most commonly used forms of disinfection technologies include: UV technology, chlorine, chloramine and ozone. Many conventional water treatments, including filtration, sedimentation and coagulation can also effectively remove viruses. Disinfectant efficacies are measured by concentration (C) in mg/l, as well as time (T) in minutes (CT value, except for UV) necessary to attain the desired logs of disinfection under the temperature and pH conditions.

  • UV technology: Proved beneficial for many years, and is still continuously rising in popularity for water treatment. UV light’s produced when an electric arc is struck in mercury. However, according to Robert Dash of Viqua UV, "The future of UV lamp technology will move away from cylindrical mercury arc lamps, and into lamps that will not contain mercury."
  • Ozone: Is an effective water treatment commonly used to reduce color, taste and odor concerns. Ozone is also used in place of, or to reduce chlorine.
  • Chlorine: Is typically an effective treatment for bacteria/viruses, but not for protozoa, especially when applied to clarified low turbidity water.
  • Chloramine: Is a reaction product of chlorine and ammonia and is less potent than chlorine; it’s known to successfully reduce Legionella counts.


There are many advantages and disadvantages of each water treatment technology available for bacteria/viruses; and sometimes a combination may be needed for success. However, ensuring your drinking water is clear of any harmful bacteria/viruses is detrimental to avoid potentially critical health threats.

You can find more information on bacteria/viruses, additional contaminants and drinking water regulations here.

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