Since conventional procedures can fail to detect coliforms in potable water, the effects of increased sampling frequency and alternative bacteriological media on coliform detection were evaluated for samples from groundwater-fed public water supply systems. For 1560 drinking water samples collected from ten small water systems in western Oregon, the Presence-Absence (P-A) test detected significantly more coliform positive samples than either the conventional Membrane Filtration (MF) test using mEndo agar-LES or the five and ten replicate Fermentation Tube (FT) test. A five-fold increase in sampling frequency increased the incidence of coliform detection 2.9 to 5.0 fold. An additional study of six hundred water samples demonstrated that five alternative coliform tests including the Presence-Absence test and four MF media formulations detected significantly more coliform positive samples than the conventional MF test under either aerobic or anaerobic conditions. Coliform densities from the m-T7 test were 1.4 to 2.1 times greater than for the other MF tests.