Microbiological growth in cooling water systems presents several challenges for water treatment providers. Culture methods such as heterotrophic plate count (HPC) and "dipslides" provide valuable information related to general microbiological water quality but require several days to produce results. Alternative methods using adenosine triphosphate (ATP) measurement provide faster results and have been applied when rapid water quality assessment is necessary. Our evaluation reviewed potential applications for ATP analysis in cooling water systems. We also assessed whether total bacteria measurement using culture methods or ATP analysis can predict the Legionella presence/absence using both experimental data and data collected from field observations.