The purpose of this study was to assess and compare selected parameters of drinking water quality monitored by state authorities and compare with water from individual ground wells not subject to official control, as well as to assess the exposure of the studied area inhabitants to nitrates, taking into account the method of treatment for the water supply. The study collected well water samples from 52 randomly selected households in Rybnik county located in south-western Poland. Nitrate concentration was determined in the tested water samples using the DR 3900 spectrophotometer. The lowest determined concentration of nitrate was; the average value was – 41.2 mg/L. This publication estimates the potential risk to human health due to consumption of drinking water from public water systems and private shallow wells in Rybnik County, Poland. In the case of well water samples HQ value was greater than 1 in 50% of samples in case of children exposure, in 40% in case of teenagers exposure and 33% in case of adults.