The diploma thesis is primarily focused on risk analysis and risk assessment of drinking water supply systems. In the research, the issues of risk analysis and risk assessment considering world and Czech Republic, were summarized. Software WaterRisk, which was developed by BUT Brno, was used for risk assessment of a particular water supply system in Třebom. Next, the thesis is aimed on technical audit of water tanks. There was a research of technical audit in the world and in the Czech Republic. Also assessment of technical audit of a particular water tank, which had to be anonymized, using software TEAwater is described in detail. Two conditions were considered: before and after reconstruction.