This dataset contains different water quality and -quantity data, collected in a small headwater catchment in the north of Hesse, Germany. Grab samples were collected manually on different sites within the stream and analysed for nutrients and stable water isotopes. On site 2, our main monitoring station, we installed probes for high frequency measurements of discharge, nitrate, and conductivity. Site 3 corresponds to the WWTP outlet. Meteorological data was collected via a meteorological station at the site of the WWTP. We also monitored the combined sewer overflow via a modified conductivity logger. CSO_on = 1 indicates, that the CSO is discharging. The data was processed and checked for quality, including sensor calibration and visual inspection, to remove obvious errors. Detailed procedures are described by Spill et al. (2023) (see Metadata)