Summary:

The article presents a hydrochemical characteristic of precipitation sewage in an urbanised catchment area. Water samples were taken at the outlet of the sewage pipe to a retention water reservoir located in Czeladź (Silesian province). Precipitation sewage were taken during spring thaw and in summer when there were heavy rainfalls during storms. It has been proved that precipitation sewage is featured by a high level of pollution both with mineral substances and biogenic elements. Besides, thaw sewage is of very high conductivity (fig. 1) reaching even 7 mS/cm. Such high conductivity results mainly from a high concentration of chlorides (fig. 3). Their source is salt used in winter to remove ice from roads. Both in spring and in summer the most polluted was the first flow of precipitation sewage washing down all the pollutants covering the catchment area.