Tap water calcium and its relationship to renal calculi and 24 h urinary calcium output in Great Britain.

Tap water calcium content in Great Britain has been re-determined and found to vary with geological age; the older the land mass the lower is the local tap water calcium content. No obvious correlation was observed between local tap water calcium content and the number of patients discharged from hospital with a first diagnosis of renal calculi. Variations in tap water calcium content were found to account for less than three per cent of the variation observed in 24 h urinary calcium output.