Project staff and volunteers conduct membrane filtration of the water samples in order to see how many fecal coliform and E. coli bacteria are in the water sample.

The water is drawn through a membrane with 0.45 micrometer pore size, effectively trapping the bacteria on the filter.

The test uses a selective and differential bacterial growth medium called mTEC. When incubated at 44.5 degrees Celsius, fecal coliform bacteria will form small yellow colonies. When the bacteria are placed on a urea substrate, only fecal coliform which are also E. coli will remain yellow. We decided to count both catagories of bacteria because each was used by a different state regulatory agency.