NSF receives many inquiries each month from consumers who are concerned about the presence of microorganisms in their drinking water, bacteria and parasites in particular. Although the presence of bacteria is usually limited to untreated water supplies, such as private or community wells with limited or no central disinfecting treatment, it is possible for microorganisms to become present in public water supplies as well, given the right conditions.
If you have ever had a bacteriological test performed, you mostly likely heard the testing laboratory refer to the presence or absence of coliform bacteria. But what are coliform bacteria and how dangerous are they?
Coliform bacteria occur naturally in the intestines of humans and animals. Although some forms of coliform, such as fecal coliform, can be infectious, they are not considered to be pathogenic or disease causing. However, their presence in water generally indicates that conditions exist in which other, more harmful forms of bacteria or viruses may be present. Because coliform bacteria are easy to culture and relatively safe to handle in a laboratory setting, the EPA chose this category of bacteria as the indicator organism to be used to determine the microbiological quality of drinking water.
Both public water utilities and private labs, including health departments, utilize the total coliform test to analyze the initial microbiological quality of the water supply being tested. If the total coliform test is negative, the microbiological quality is considered good at the sampling point. If a total coliform test is confirmed positive, additional testing can be performed for other forms of bacteria, such as fecal coliform or E. coli. This is especially common on private well supplies, as detection of these bacteria in the well water supply can indicate a problem with a nearby septic field.
Similar to bacteria, cysts live in the intestines of humans and animals. However, cysts are classified as protozoa, not bacteria. Because they have a protective outer shell, they are generally immune to the effects of chlorine and other chemical agents commonly used to disinfect drinking water. However, this same protective shell means that cysts cannot readily change their shape or size as bacteria can, allowing them to be effectively removed from drinking water through some non-chemical forms of treatment, such as Filtration.
There are several options homeowners can use to disinfect their incoming water supplies if they suspect bacteria are present.
Microbiological testing is an important part of maintaining water quality. Municipalities are required to test for bacteria on a regular basis, and any violation of microbiological standards will result in a boil water notice being issued. It is important that consumers with private wells also perform bacteriological testing at least annually.
If you have a Filtration device installed and want to determine what capabilities it may have to protect you against bacteria or other contaminants, contact the manufacturer or see if the product is certified by an independent lab for that purpose. It is important that systems be installed and operated according to the manufacturer's instructions. For example, some manufacturers advise not to use their home water treatment device on water supplies known to contain bacteria. Some systems may need to be disinfected and the filter components replaced if they are accidentally exposed to microbiologically contaminated water.
Consumers are welcome to contact our Consumer Affairs Office (1-800-673-8010 or via email at email@example.com) for further information or answers to questions about microorganisms in drinking water and options for treatment. Additional information on drinking water and home water treatment products is also available in our Drinking Water section.