Effects of water hardness on urinary risk factors for kidney stones in patients with idiopathic nephrolithiasis

Both amount and timing of dietary calcium intake influence the recurrence o f renal calcium stones. We have evaluated whether the hardness of extra mea l drinking water modifies the risk for calcium stones. The urinary levels o f calcium, oxalate and citrate, i,e,, the main urinary risk factors for cal cium stones, were measured in 18 patients with idiopathic nephrolithiasis, maintained at fixed dietary intake of calcium (800 mg/day), after drinking for 1 week 2 liters per day, between meals, of tap water and at the end of 1 week of the same amount of bottled hard (Ca2+ 255 mg/l) or soft (Ca2+ 22 mg/l, Fiuggi water) water, in a double-blind randomized, crossover fashion. As compared with both tap and soft water, hard water was associated with a significant 50% increase of the urinary calcium concentration in the absen ce of changes of oxalate excretion; the calcium-citrate index revealed a si gnificant threefold increase during ingestion of hard water as compared wit h respect to soft water (Fiuggi water), making the latter preferable even w hen compared with tap water. This study suggests that, in the preventive ap proach to calcium nephrolithiasis, the extra meal intake of soft water is p referable to hard water, since it is associated with a lower risk for recur rence of calcium stones.