We are the inspecting authority for the state of Texas under the Safe
Drinking Water Act, and have been performing that function since 1976.
EPA mandates sampling plans for public water systems in the United States,
so we have no experience with altered sampling plans. However, since the
sampling takes place only once a month, in most cases, you are relying on
the philosophy that you are measuring over system efficiency in
performance, rather than hoping to catch that random system failure (if it
weren't random, you would quickly learn by epidemiological information).
If you have flexibility in your code, I would suggest that the best way to
economize would be to continue total coliform testing, using the least
expensive process you can find, and deleting the fecal coliform test. The
fecal coli test provides good differentiation if you need it, but your
desire is to so control the system that you will not need to
differentiate, because your samples will be absent coliforms altogether.
Hope this is helpful.