This dataset presents the characteristics of sidestreams that result from the settling, thickening and dewatering of sewage sludge. These data have been collected from the scientific literature and all available characteristics (volume and concentrations of different components) have been included. The origin of the data is systematically presented. The collected dataset is organised by source of sidestreams: thickening of primary sludge, thickening of biological sludge, dewatering of digested sludge, dewatering of digested sludge pretreated through a thermal hydrolysis process. More information about the configuration of the water resource recovery facilities (WRRFs) are provided when available: secondary treatment type, specific phosphorus treatment type and dewatering or thickening equipment. This dataset allows the calculation of statistical information for each observed characteristic. These data can be useful to researchers, engineers and WRRF operators because they are scarce at full-scale. This dataset can be an easy-to-use resource for improving knowledge about sidestream characteristics.