Coliform bacteria are not necessarily disease producing themselves but can be indicators of organisms that cause adverse health effects. Escherichia coli (E. coli) are bacteria that live in the intestines of people and animals (i.e., fecal coliform indicator). The confirmed presence of E. Coli bacteria indicates that infectious microorganisms maybe in your water. Most strains of E. coli bacteria are harmless although certain strains cause illnesses.