E. coli is a sub-group of the fecal coliform bacteria group. There are many strains of E. coli, most of which are harmless, but some strains can cause illness. E. coli outbreaks receive much media coverage. Most outbreaks have been related to food contamination (not water) caused by a specific strain of E. coli known as E. coli O157:H7.
When a drinking water sample is reported as "E. coli positive," it does not mean that this specific strain is present and in fact, it is probably not present. However, it does indicate recent fecal contamination. Boiling or treating contaminated drinking water with a disinfectant destroys all forms of E. coli, including O157:H7.