Escherichia coli (E. coli) is a species of bacteria that is naturally found in the intestinal system of humans and animals. It is present in feces in high numbers and can be easily measured in water, which makes it a useful indicator of fecal contamination for drinking water providers. E. coli is the most widely used indicator for detecting fecal contamination in drinking water supplies worldwide. In drinking water monitoring programs, E. coli testing is used to provide information on the quality of the source water, the adequacy of treatment and the safety of the drinking water distributed to the consumer.