Water quality is the most important parameter related to water intended for human consumption. The main task of water supply companies is to keep water quality at the possible highest level. Water, which consumers receive in their homes, is the final product of a multi-stage processing, which aims to obtain water with the required physico-chemical and biological composition. Nevertheless, during transport through the Water Supply System (WSS), water reacts with various factors, sometimes causing secondary pollution. An important threat associated with water quality reduction is disinfection by-products (DBP), formed during the oxidation of organic compounds and some inorganic compounds found in water. DBPs has carcinogenic properties, that's why they are threats for human health.The article presents the results of water quality analysis and risk assessments. In research the real WSS, which supplies water to selected Silesian agglomeration, was analyzed. The work uses laboratory tests of selected water parameters. Statistical methods were used to determine the causes of water quality deterioration.
