Drinking water for stone formers: is the calcium content relevant?

Stone formers are often told to select a drinking water with low Ca content. To see whether this measure has a rational biochemical background, 4 Ca hyperabsorbers were asked to drink, first tap water ad libitum, then 2 liters/day of tap water, then 2 liters/day of a low Ca water (A) and finally 2 liters/day of a high Ca water (B). On A, subjects were normocalciuric but hyperoxaluric; whereas on B, they were markedly hypercalciuric but normooxaluric. Therefore, Ca . Ox concentration products were similar on B and A. However, on A as well as on B, Ca . Ox products were much lower than on tap water ad libitum due to the high fluid intake which had thus been imposed. It is concluded that, in the prevention of the recurrence of nephrolithiasis, 'have a high fluid intake' is probably a more relevant advice than 'select a water with a particularly low Ca content'.