Rapid determination of bacteria in drinking water using an ATP assay

The presently used heterotrophic plate count (HPC) for the evaluation of the total number of bacteria in a sample of drinking water takes 7 days of incubation. When the results are known, the water has been consumed and is ineffective for the protection of the health of the consumers. Operators of water treatment systems need to know the bacterial water quality in near real time. Contamination of the system, whether it is intentional, accidental, or due to an inadequate disinfectant residual needs to be discovered much sooner because intervention can then take place in the form of flushing low quality water and/or raising the disinfectant residual. The purpose of this study was therefore to determine if a rapid ATP assay can estimate the HPC in minutes. Two additional methods were used for some samples. The first method was the acridine orange direct count (AODC) that enumerates both viable and nonviable bacteria. The second method was the direct viable count (DVC) that enumerates only viable bacteria. Water samples were obtained from local, national, and international locations. The sample selection criteria were based on proximity to the laboratory, cooperating water utilities, and the travel of the authors. The results of the study show that the rapid ATP assay is highly correlated with the conventional plate count method and the DVC method. The significance of the ATP assay is that it can determine the bacterial quality of the drinking water in less than 5 min. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 185–189, 2001