Solute budgets and within system variations in water chemistry have been studied at three catchments in western Britain. The solute budgets showed a net export of calcium and silica from all three sites and of aluminium and magnesium from two. Hydrogen ion budgets, based on bulk precipitation inputs and streamwater outputs, underestimated inputs of acidity and fail to take account of within system sources. At two sites the aluminium and silica were derived from the soils and the calcium and magnesium from the bedrock compartment. There was little, if any, weathering of the mudstone and slate bedrocks at these two sites; calcium and magnesium were derived from carbonate veins and/or dolerite intrusions. At the third site, aluminium and silica were released from the upper soil, and calcium and magnesium from the lower soil or underlying, calcareous till. Catchment hydrology was, a major factor influencing the pattern and rate of weathering.