Monitoring SARS-CoV-2 presence in wastewater has been carried out since April 2020, when the new disease COVID-19 began to spread rapidly in the Czech Republic. The aim of this study was to detect viruses in order to evaluate the possibility of using wastewater analysis as one of the tools for the establishment of an early warning system. As a complement to SARS-CoV-2 RNA detection, noroviruses and adenoviruses were detected, as well. In the first round of monitoring, which took place from April to June 2020, a total of 122 samples of untreated wastewater were collected from 35 WWTPs of different size within the Czech Republic. Viral RNA was concentrated from wastewater and RT-PCR was used to detect RNA of viruses. SARS-CoV-2 RNA was found in 15 % of all samples, noroviruses in 43 % and adenoviruses in 95 %. It was confirmed that even low amounts of SARS-CoV-2 RNA in wastewater might be detected. Our data indicate that wastewater analysis may be a suitable tool for the establishment of early warning system. However, for unambiguous interpretation of data, it is necessary to evaluate other factors that might significantly influence the concentration of viral RNA in wastewater.