Patients with recurrent calcium oxalate stones undergoing endourological procedures for renal stones at our institution from June 2013 to June 2014 were considered eligible for enrolment. Enrolled patients underwent a baseline unenhanced CT scan before the urological procedure; after endoscopic removal of their stones, the patients were instructed to drink at least 2 L/day of a hypotonic, oligomineral water low in sodium and minerals (fixed residue at 180°C <200 mg/L) for at least 12 months. Finally, the patients underwent a follow-up unenhanced CT scan during hydration regimen.

Inclusion Criteria:

• Patients undergoing endourological procedures for renal stones
• Recurrent stone disease
• Calcium oxalate stones (>50% of the stone made of calcium oxalate)

Exclusion Criteria:

• Systemic conditions causing stones (hyperparathyroidism, intestinal malabsorption, renal tubular acidosis)
• Non-calcium oxalate stones