The BGS groundwater levels dataset is a gridded interpolation of depth to groundwater. The dataset is a raster grid, with 50 × 50 metre pixels holding values that represent the probable maximum depth, in metres, to the phreatic water table. This represents the likely lowest water level, under natural conditions, in an open well or borehole drilled into the uppermost parts of a rock unit. The dataset has been modelled from topography and hydrology, assuming that surface water and groundwater are hydraulically connected. It has not used observations of groundwater level in wells or boreholes directly, but they have been used to validate its performance.