The article deals with the use of rainbow trout as a bioindicator of drinking water quality. The first part summarizes the main principles of rainbow trout rearing, testing of water quality, histological and chemical analyses of fish. The second part describes the use of rainbow trout in the Podoli water treatment plant (Prague, Czech Republic). The fish is put into tanks with purified water at the age between 3 and 6 months and reared untill one year of age. Contamination of fish tissues is then monitored. The results obtained during the last years show that the water quality in this purification plant is very good as the concentrations of the studied contaminants in fish tissues has been much below the maximum residue limits.