A Cochrane review included one study with a total of 199 subjects. The recurrence rate of urinary stones was lower in the increased water intake group than that of the no intervention group (12% versus 27%, RR 0.45, 95% CI 0.24 to 0.84). The average interval for recurrences was 3.23 ± 1.1 years in increased water intake group and 2.09 ± 1.37 years in the no intervention group (MD 1.14, 95% CI 0.33 to 1.95). No trials of increased water intake for the primary prevention of urinary calculi met the inclusion criteria.
Comment: The quality of evidence is downgraded by imprecise results (few patients and wide confidence intervals).