This dataset is a compilation of water quality data for the River Frome catchment, Dorset, UK. The data have been sourced from the Environment Agency and from Wessex Water Ltd., the water utility company for the catchment area. The monitoring sites are specifically located in the lower part of the River Frome, between the Environment Agency gauging stations at Dorchester and East Stoke. The dataset includes water quality measurements for boreholes, sewage treatment work (STW) final effluents, tributaries, and main river channels. In total there are 21 monitoring sites. Water quality measurements date from 1976 to 2022. The main river channel and tributary sites are typically monitored on a monthly basis and the STW final effluents typically on a weekly basis. The borehole data can vary from weekly to monthly, depending on the determinand and borehole measured. Full details about this dataset can be found at https://doi.org/10.5285/9d98e1a7-7602-490f-9896-0eeed6eb1d40