The control of drinking water microbial quality and disinfection efficiency is usually performed using the conventional heterotrophic plate count method. The latter method has several shortcomings such as the long time required for analyses and the fact that less than 1% of water bacteria are cultivable on agar plates. The ATP method is based on ATP’s role as an energy source in bacterial metabolism, thus directly linking it to bacterial viability. Some previous studies have demonstrated ATP as a prospective tool for bacterial viability assessment in drinking water. However, the method should be used with certain prudence when analyzing water what underwent oxidative disinfection, as increased extracellular ATP values were often observed after ozone and chlorine exposure during drinking water treatment. The primary goals of the present study were therefore the investigation of (1) ATP release during chlorination, and (2) the stability/degradation of extracellular ATP in the water matrix. Firstly, we investigated extracellular ATP release from indigenous microbial communities under different chlorine doses. The obtained results showed that in the case of the strong chlorination, all intracellular ATP was released concurrent with bacterial lysis, while for low chlorine concentrations a decrease of intracellular ATP occurred with only negligible external release. Secondly, we observed that extracellular ATP molecules were stable for up to 20h in sterile water, but was rapidly degraded in presence of indigenous bacterial communities. The combined data showed that an understanding of intracellular ATP depletion and extracellular release during oxidative disinfection, as well as microbial degradation of such extracellular ATP, allows for the use of this method to monitor disinfection, biological stability and bacterial regrowth in chlorinated drinking water.