Escherichia coli should not be detected/present in any drinking water sample. Escherichia coli is a fecal coliform and can be detected using methods such as membrane filtration, presence/absence and MPN. Since Escherichia coli is present in fecal matter and prevalent in sewage, but is rapidly destroyed by chlorine, it is a strong indicator of recent fecal pollution. Contamination with sewage as shown by positive E-coli tests would strongly suggest presence of pathogenic bacteria and viruses, as well as more chlorine resistant pathogens such as Giardia and Cryptosporidium, which are much more difficult to detect.