A rapid and sensitive method for the detection of low levels of bacteria in potable water was developed. The fecal indicator bacterium Escherichia coli was used as the test organism in a filtration concentration - nested polymerase chain reaction (PCR) protocol, combined with ethidium bromide visualization of PCR products. Two sets of primers were designed from the E. coli specific beta-glucuronidase gene (uidA), the primary pair producing a 486-bp fragment that was used as template for the nested primer pair delineating a 186-bp fragment. This protocol can detect 1-10 bacterial cells/50 mL water sample within 6-8 h, in contrast to traditional culturing or Southern hybridization methods which require 2-3 days for results.