Why test water for coliform bacteria rather than for pathogenic bacteria which maybe present?

It's much easier to test for coliform bacteria and the test is considered presumptive. That is, if coliform bacteria are present, pathogenic bacteria MAY be present. So absence of the more general bacteria will suffice to prove absence of the pathogenic bacteria.

Why test water for coliform bacteria rather than for pathogenic bacteria which maybe present?
Coliform is the common bacteria found in human waste. Testing waters for that will see if there are elevated levels greater than what in naturally present. If there is a concern of higher level of pathogenic bacteria, such as "red tide", then that would/should be tested for.
Reply:as it has already been said, it is easy to test the coliform count, and with that an assumption can be made about the presence of pathogenic microorganisms. other than that, coliform survives in the same conditions as most pathogenic bacteria, so the presence of coliform in a tested water suggests that a pathogenic bacteria can survive as well. and there are multitude of pathogenic bacteria out there, each with unique tests for their presence, so it takes a longer time to test for the pathogens. so coliform testing is both easy and fast way of identifying the presence of pathogens in water.hope this helps...