Finding E. coli bacteria in water is an indication of fecal contamination. E. coli are always present in large numbers in feces and live a long time outside the body. Rather than testing for all possible organisms, testing for E. Coli will tell if the water is safe to drink. The World Health Organization recommends testing for this organism as the method of choice for detecting fecal contamination of water.
Two newer methods of testing for E. coli bacteria are the Colilert tube made by IDEXX and the Petrifilm plate from 3M. One ml. of water is spread on the Petrifilm plate and 10 mls. Of water are placed in the IDEXX Colilert tube. After incubating at body temperature for 24 hours, easy to interpret results will show if E. coli bacteria are present in the water.