How do we KNOW that there aren’t
any pathogens in our drinking water or in the water down at the
old swimming hole? There are so many different kinds of organisms
that cause diseases that it would be too expensive and time consuming
to test for each one.
Diseases are spread when water is contaminated with fecal matter.
We can test for that pollution by using indicator
These are microbes whose presence in water signals the presence
of fecal matter, and potentially, pathogens. One such indicator
organism is Escherichia coli, a bacterium that is normally found
in the guts of humans and other warm-blooded animals. Water that
is highly polluted with fecal matter may have E. coli counts
in the tens of millions of bacteria per liter. In the State of
Michigan, beaches are ordered closed if the E. coli count exceeds
a monthly average of 130 or a maximum of 300 bacteria per 100
milliliters. A drinking water source is declared safe only if
these bacteria are not detected in the sample.