ASSESSMENT OF DRINKING WATER QUALITY BY PHYSICAL AND CHEMICAL PARAMETERS OF A WATER SOURCE
Background. The object of the study is the water treatment system of the St Petersburg Vodokanal (water supply system), which is controlled by seven drinking water quality indicators depending on six physical-chemical parameters of water and two managed parameters (dose of a coagulant and a flocculant used in water purification). The subject of the research is the quality of drinking water. The aim of the study is to develop an early warning system for possible water quality loss due to deterioration of physico-chemical indicators of a water source (forecasting a possibility that one or more water quality indicators will be over the permissible limit) and to control activities (changing doses of a coagulant and a flocculant) to avoid emergency situations. Materials and methods. The study of water quality was conducted by building regression models that best represent the dependence of drinking water quality indicators on physico-chemical parameters and controlled parameters, on the basis of monitoring of water treatment systems. Results. The authors developed models for drinking water quality indicators that can be used to predict the future state of drinking water. Conclusions. As a result of regression modelling of drinking water quality indicators it has been found that global models do not provide the necessary accuracy of forecasting. In order to enhance the value of the determination coefficient it is suggested to use small samples applying piecewise-linear regressions taking into account autoregressions of the second order. To assess the effect of controlled agents (doses of a coagulant and a flocculant) on water quality indicators, the authors recommend to use piecewise quadratic models. The proposed approaches will allow to prediction the potential of emergency situations at which the selected indicators of drinking water quality may go over the permissible limit.