Bacteria in our Drinking Water

  1. Not all bacteria are bad for water health and the quality of our drinking water!
  2. The Environmental Protection Agency (EPA) sets maximum contaminant level goals (MCLGs) and maximum contaminant levels (MCLs) for each potential drinking water contaminant.
  3. MCLGs are the non-enforceable levels of a specific contaminant in drinking water below which there are no known health risks. MCLs are enforced standards that are the highest allowed levels of a specific contaminant in drinking water.
  4. Water treatment plants often use chlorine as a disinfectant, but due to possible side effects, chlorine levels are also regulated by the EPA.
  5. It is inefficient and largely unfeasible to try to identify all of the potential pathogens that a body of water may contain; therefore, water quality assessment centers around the detection of non-pathogenic bacteria that act as indicators for the presence of other types of harmful bacteria.
  6. Indicators include total coliform and enterococcus bacteria, and are usually used to determine fecal contamination in water.
  7. Total coliform bacteria are found in both feces and the environment, and can be used to assess the effectiveness of water treatment and the overall cleanliness of the water body. As many of the coliforms identified through coliform detection assays are not of fecal origin, the EPA considers coliforms to be indicative of a potential pathway of contamination but not an actual health threat.
  8. E. coli is by itself a very reliable index of fecal contamination, because it is present in feces at very high numbers. The EPA’s Maximum Contaminant Level Goal for E. coli is zero, while the maximum contaminant level specifies that no more than 5 % of samples from a given water body may be positive in one month.
This factsheet is adapted from information provided by the World Health Organization (WHO) and the Environmental Protection Agency (EPA). Retrieved from ;