Lack of correlation between water hardness and salivary calculi in England.

Our aim was to test the hypothesis that residents of hard water areas are at increased risk of developing salivary calculi. The evidence based on figures from the Hospital Episode Statistics database for the years 1991 to 1994, suggests that there is no such association. For example, in the South West Water area (soft water) the incidence was 28.92/million/year compared with Yorkshire (hard water) 31.64/million/year. The correlation coefficient shows that water hardness is not significantly associated with either the incidence of salivary calculi (r = 0.02, P = 0.9) or that of sialadenitis (n = 2.4, P = 0.4). The lack of association holds for both men and women independently. However, the two conditions have similar patterns of incidence (r = 0.5, P = 0.05), suggesting some common but unknown similarity in aetiology.