The
coliform bacteria in our
intestines aid in the
digestion of
food. This particular subgroup is associated with the
fecal matter of
warm-blooded animals. The bacteria in and of themselves don't really pose a
health threat to
human beings- but don't get your
swim trunks on yet.
The detection of fecal coliform bacteria in water is used mainly as a public health flag for the other nasty pathogens existing in fecal material: typhoid, hepatitis A, dysentery, cholera, and gastroenteritis, for example.
The main sources of contamination in waterways are sewer overflows, treatment plant failure, septic tank failure, plus agricultural runoff, urban runoff, and wildlife (where rain sends animal waste into the waterways).