Justification of temporary deviations from the standardized indicators of drinking water quality

the absence of a threat to health should be confirmed through a risk assessment, which is associated with methodological difficulties. Materials and methods. Health risk assessment projects from drinking water consumption of centralized drinking and household water supply systems in two settlements. The results of laboratory studies of drinking water quality using descriptive statistics methods are analyzed. The health risk assessment was carried out in accordance with the current guidelines G 2.1.10.1920–04. Results. According to the results of laboratory studies, it was found that the quality of drinking water before being supplied to the distribution network of settlement No. 1 didn`t meet the requirements of hygienic standards in terms of total hardness and strontium, settlement No. 2 – in terms of «total hardness», «dry residue», «magnesium», «bromine», «boron», while all these indicators, with the exception of total hardness exceeded the MPC by no more than an error of the determination method. In this regard, temporary deviations were justified only for the «total hardness». Non-carcinogenic risk assessment showed that the values of the hazard coefficients corresponded to the permissible level. The levels of the total carcinogenic risk by consumption of the drinking water throughout whole life and for 7 years correspond to the upper limit of acceptable risk. Limitations. The limitation was the number of laboratory test protocols selected for analysis – over a 3-year period. In addition, the limitation was the inability to evaluate the full list of indicators from the point of view of risk assessment, as well as the probabilistic nature of the results obtained. Conclusion. To justify temporary deviations in drinking water quality in terms of «total hardness», it is necessary to conduct a complete study of the concentrations of cations forming the «total hardness» indicator – magnesium, calcium, strontium, and barium using a health risk assessment.