If your drinking water does not come from a public water system, or you get your drinking water from a household well, you alone are responsible for assuring that it is safe. A standard water sample tests for Coliform and E Coli bacteria.
If your water source is a well, and/or your home will be financed with a FHA or VA loan, the lender will most likely require a water test. In most cases, FHA/VA will require that the sample is drawn by a home inspector or county health department official to ensure the chain of custody is followed, and to ensure that the sample is tested using the proper testing protocol. The FHA/VA Scan tests for coliform, lead, nitrates and nitrites.
The-Home Inspector will sample your water and take it directly to a certified lab for testing. A report will provide detail of the results.