Hydration to Prevent Kidney Stones | Sydney Kidney Stone Clinic

The target

Clinical guidelines recommend aiming for a daily urine output of around 2.5 L, spread evenly over 24 hours.¹ In most climates and most body sizes that means drinking roughly 2.5 to 3 L of fluid a day - more in hot weather or with heavy exercise, because some fluid is lost through sweat.

How to know whether you are hitting the target

Pale, straw-coloured urine throughout the day is the best bedside indicator.
Dark yellow urine, or passing small volumes of strongly-coloured urine, means the target is not being hit.
Passing urine roughly every 2-3 hours during the day is another useful marker.
If motivated, a 24-hour urine collection gives an exact figure. Dr Kooner's rooms can arrange this if a metabolic workup is in progress.

Practical tips

Keep a bottle with you. The most common reason for missing the target is simply forgetting to drink.
Spread fluid through the day. Three litres drunk in the evening will not prevent overnight concentration of urine.
Drink a glass of water before bed and another on waking - the overnight period is when urine is most concentrated.
Extra fluid with exercise and in hot weather. Aim for urine output of 2.5 L - not just intake. In a hot climate you may need 3.5-4 L to reach that.
Plan for travel. Long-haul flights and extended drives are common triggers for a stone episode.

What to drink

Plain water is the most practical choice for most people. Other options:

Diluted lemon or lime juice adds natural citrate, which inhibits calcium stone formation. Evidence from randomised trials is modest but the biological rationale is sound.²
Mineral water with a moderate bicarbonate content is acceptable.
Coffee and tea in moderation are fine and contribute to fluid intake. Very strong tea is a source of oxalate, so patients with recurrent calcium oxalate stones should not drink more than about 2-3 cups a day.
Alcohol should be moderate. Beer in particular is a diuretic (causing loss of fluid) and the dehydration that follows a heavy drinking session is a classic trigger.

What to avoid

Sugar-sweetened soft drinks have been associated with a higher stone risk in some cohort studies. Unsweetened is preferred.
High-sodium sports drinks in excess - occasional use is fine, but water is a better default.
Very concentrated fruit juices can be high in oxalate (cranberry, apple) - small amounts, well diluted, are fine.

Does hydration alone prevent stones?

In the right patient, hydration alone is a powerful intervention. But it only works if it is sustained. The 2026 Scales trial of a structured adherence programme found that it modestly increased urine volume but did not significantly reduce symptomatic recurrence (HR 0.96, 95% CI 0.77-1.20), underlining that the real-world benefit depends on actually hitting and holding the target day in, day out.³

Using a fluid chart

Some patients find a simple fluid-intake chart helpful for the first few weeks - ticking off every glass through the day turns a vague intention into a measurable routine. A printable chart is below.

Fluid input/output chart PDF - BAUS patient brochure

References

Skolarikos A, et al. EAU Guidelines on Urolithiasis. 2025.
Nabi R, et al. The role of citrus juice in reducing calcium kidney stone risk: systematic review and meta-analysis. African Journal of Urology. 2025;31:70.
Scales CD Jr, et al. Prevention of urinary stones with hydration: a randomised clinical trial of an adherence intervention. 2026.

Hydration