In this study, scientists analyzed 3,413 wastewater samples from 94 municipal catchments, covering more than 59% of the Austrian population between December 2020 and February 2022. They used quantitative PCR (qPCR)-based approache, in which viral RNA was first transcribed into the complementary DNA sequence (reverse transcription). This DNA was amplified in a second step. The amplification step is important to obtain sufficient material for sequencing. The sequencing method must be very accurate to detect mutations in the DNA that are specific to certain virus variants. This is called deep sequencing, and means that a genomic region is sequenced multiple times, sometimes hundreds or even thousands of times. The challenge is to analyze this sequencing data for the regional occurrence of specific variants (a total of 33 variants were included in the analysis). They began by grouping the detected mutations into mutations for specific variants and created a comprehensive set of marker mutations. This allowed them to develop a method, which they named VaQuERo (variant quantification in sewage designed for robustness), to detect and quantify the variant composition in the wastewater over time. Moreover, to visualize the regional patterns of expansion and decline of single variants, they reduced Austria to its main axis of mobility (west-east and east-south direction) and were thus able to generate a space-time coordinate system. This was demonstrated by the steady retreat of B.1.160 and B.1.258 and their replacement by Alpha, which began in January 2021 in the eastern provinces of Austria and was completed only about three months later in the western provinces. The displacements of Alpha by the Delta variant in early summer 2021 and subsequently of Delta by Omicron in winter 2021/22 began almost simultaneously throughout Austria and were completed within one month.