We present a large and unique dataset of the rainfall isotopic composition at seven sites from northern Iberia to characterize their variability at daily and monthly timescales and to assess the role of climate and geographic factors in the modulation of δ¹⁸O values. We found that the origin, moisture uptake along the trajectory and type of precipitation play a key role. These results will help to improve the interpretation of δ¹⁸O paleorecords from lacustrine carbonates or speleothems.