This study compared the results of standard plate counts with those of the combined acridine orange (AO) and 2-(p- iodophenyl)-3-(pnitrophenyl)-5-phenyl-tetrazolium chloride (INT), or AOINT, technique for samples of distribution water and well water. To overcome the interference of a membrane filter's pores with the identification of stained cells, the authors used a gel-stripping technique to transfer the bacterial cells from membrane filters to a gelatin matrix before counts were made. Results show that the use of the AOINT technique provides a rapid and sensitive method for the determination of total numbers of metabolically active bacteria in a water sample, making it a useful adjunct to standard plating for monitoring problematic water supplies. In addition, water supply contamination can be detected in 4 hours using the AOINT technique. Includes 25 references, tables, figure.