These data are based on the UK rainfall chemistry data held on the UK-AIR database operated on behalf of Defra (http://uk-air.defra.gov.uk/). A subset of 20 sites was analysed, being those with the longest continuous data record from 1986 to 2011. Rainfall samples from bulk collectors were taken weekly or two-weekly at sites across the UK and analyzed by a central laboratory. The raw reported data contain some samples which were contaminated by bird droppings, or by wind-blown dust, and should not be used to estimate annual or long-term wet deposition at the measurement sites. Some samples were missing for other reasons, such as physical loss of the rain sample prior to analysis. Following identification and removal of contaminated sample data, the missing data were estimated, where possible, using statistical interpolation across both time and space with the GENSTAT procedure MULTMISSING. The final datasets contain the accepted and estimated data values, flagged as appropriate. The data filenames correspond to the sites as listed in the UK-AIR database (Allt a'Mharcaidh, Bannisdale, Barcombe Mills, Bottesford, Eskdalemuir, Flatford Mill, Goonhilly, High Muffles, Hillsborough, Loch Dee, Lough Navar, Preston Montford, Pumlumon, Stoke Ferry, Strathvaich, Thorganby, Tycanol Wood,Wardlow Hay Cop, Whiteadder, Yarner Wood). This cleaned dataset was prepared by Neil Cape, Ron Smith and David Leaver at CEH Edinburgh on behalf of Defra and the Devolved Administrations under the project Pollutant Deposition Processes. Full details about this dataset can be found at https://doi.org/10.5285/ada39609-ddec-4cbe-85c2-4fdd6bd774d7