The role of increased fluid intake as a means of preventing recurrence of kidney stones is well recognized today. In fact, it has been used since the time of Hippocrates.
Adequate fluid intake helps to decrease concentrations of substances involved in stone formation thus reducing their saturation degree in urine (a necessary condition for crystallization, and a first step towards stone formation).
Many studies have shown the beneficial effects of improved fluid intake (and consequently urine volume) on stone recurrence prevention.
The strongest scientific evidence certainly comes from a five-year randomized controlled trial conducted amongst patients recruited directly after their first idiopathic calcium stone episode. This study showed that recommending patients to increase fluid intakes to achieve a urine volume superior to 2L per day resulted in reduced kidney stone recurrence compared to a group without specific advice.1
The European Association of Urology2 recommends increasing fluid intake independent of the type of stones to achieve a urine volume of more than 2L a day, on top of other dietary and lifestyle advice.