The assessment of drinking water disinfection efficiency traditionally involves the estimation of faecal indicator inactivation rates in the form of reduction of cultivable counts. Widely described, viable but noncultivable (VBNC) state as a form of bacterial survival strategy in oligotrophic conditions is not considered in these estimations. The aim of the present research is to assess the effect of free chlorine disinfection on faecal indicator Escherichia coli in order to study the succession of cellular alterations in response to chlorine exposure. To determine the inactivation rates, cell ability to form colonies, ability to divide as such and metabolic activity have studied. 0.064 mg/L min-1 free chlorine has been needed to obtain 99 % inactivation of cultivable counts; however, 5 till 200 times higher disinfectant dose x contact time has been required to reduce cell ability to divide and metabolic activity, respectively. The results have shown that to determine correct drinking water disinfectant doses multiple cell viability parameters should be analyzed.