To pass a kidney stone, you should drink enough water to produce at least 2 to 2.5 liters (roughly 68 to 85 ounces) of urine per day. That typically means drinking about 3 liters of fluid daily, since some water is lost through sweat and breathing. This volume keeps urine dilute, increases flow through the ureter, and gives the stone the best chance of moving on its own.
Why Water Helps a Stone Pass
A kidney stone gets stuck when urine flow isn’t strong enough to push it through the narrow tube (ureter) connecting your kidney to your bladder. When you drink more water, your kidneys produce more urine, and that increased volume creates steady pressure behind the stone. Think of it like turning up the faucet to flush debris through a pipe.
Low fluid intake does the opposite. It concentrates your urine, slows flow, and can even allow new mineral crystals to deposit on an existing stone, making it larger. Staying well-hydrated keeps urine dilute enough to prevent that buildup while maintaining the flow needed to nudge the stone along.
How Much Water You Actually Need
The target isn’t measured in glasses of water. It’s measured in urine output. Both the American Urological Association and the European Association of Urology recommend producing at least 2.5 liters of urine over 24 hours. For most people, that means drinking roughly 2.5 to 3 liters (about 80 to 100 ounces) of fluid per day, though you may need more if you’re active, live in a hot climate, or sweat heavily.
A simple way to gauge whether you’re on track: your urine should be pale yellow or nearly clear throughout the day. If it looks dark or concentrated, you need more fluid.
Spread Your Fluids Throughout the Day and Night
Drinking all your water during the morning and then stopping won’t cut it. Urine concentration spikes overnight when most people aren’t drinking, and that’s when stones are most likely to grow or stall. The University of Chicago Kidney Stone Program recommends about 5 ounces per hour even during sleep, totaling roughly 40 ounces (1.2 liters) over an eight-hour night. In practice, this means drinking a full glass of water right before bed and again if you wake up during the night.
During waking hours, sipping consistently is more effective than gulping large amounts at once. Keep a water bottle nearby and aim for steady intake rather than catching up in bursts.
What Counts Toward Your Fluid Goal
Water is the simplest and safest choice, but it’s not the only fluid that counts. Coffee appears to have a protective effect against stone formation, likely because caffeine increases urine flow. A large population study found that caffeine from coffee was associated with lower kidney stone risk, though caffeine from non-coffee sources didn’t show the same benefit.
Citrus juices can also help. Orange juice raises urinary citrate levels and makes urine more alkaline, both of which discourage stone formation. Lemon juice increases citrate too, though it doesn’t significantly change urine pH. If you’re adding citrus to your routine, lemon water is a reasonable everyday option, while orange juice carries more sugar and slightly raises oxalate levels in urine, which could be a concern for calcium oxalate stone formers.
Avoid sugary sodas and heavily sweetened drinks. They add calories without offering the protective chemistry of citrus or coffee, and some evidence links them to higher stone risk.
Your Stone’s Size Determines the Odds
Hydration matters, but the single biggest factor in whether a stone passes on its own is its width. A European Radiology study tracked nearly 400 stones and found stark differences in spontaneous passage rates over 20 weeks:
- Under 2.5 mm: 98% passed without intervention
- 2.5 to 3.4 mm: 98% passed
- 3.5 to 4.4 mm: 81% passed
- 4.5 to 5.4 mm: 65% passed
- 5.5 to 6.4 mm: 33% passed
- 6.5 mm or larger: only 9% passed
If your stone is under 4 mm, aggressive hydration gives you excellent odds. Stones between 4 and 6 mm are a coin flip, and anything larger than 6.5 mm will almost certainly need a procedure. Your doctor will usually confirm stone size with imaging before recommending a watch-and-wait approach.
How Long Passing a Stone Takes
Smaller stones (under 4 mm) often pass within one to two weeks. Larger stones in the 4 to 6 mm range can take two to three weeks. Once a stone drops from the ureter into the bladder, it typically passes within a few days, and that final stretch is usually much less painful.
About 80% of kidney stones pass on their own with hydration and time. If yours hasn’t moved after four to six weeks, your doctor will likely recommend a procedure to remove or break it up. Waiting longer than that risks damage to the kidney from prolonged blockage.
Signs That Water Alone Isn’t Enough
Hydration is the cornerstone of conservative stone management, but certain symptoms mean you need medical help regardless of how much you’re drinking. Fever or chills suggest infection behind the blockage, which can become dangerous quickly. Vomiting that prevents you from keeping fluids down defeats the purpose of hydration therapy entirely. Pain that doesn’t respond to over-the-counter medication, or that keeps escalating, signals that the stone may be too large or too lodged to pass naturally.
Visible blood in your urine is common with kidney stones and isn’t automatically an emergency, but combined with any of the symptoms above, it warrants urgent evaluation. Deteriorating kidney function, which your doctor can check with blood work, is another reason to move beyond the hydration-and-wait strategy.
Practical Tips for Hitting Your Water Target
Drinking 80 to 100 ounces a day sounds like a lot if you’re not used to it. A few strategies make it easier. Start by filling a large bottle (32 or 40 ounces) in the morning and finishing it by lunch, then refilling for the afternoon. Add lemon slices or a splash of citrus juice for flavor and a small citrate boost. Set a timer on your phone for every hour as a reminder to take a few sips, especially during the workday when it’s easy to forget.
At night, keep a glass of water on your nightstand. If you wake up to use the bathroom (which you likely will, given the volume you’re drinking), take several sips before going back to sleep. That overnight hydration helps maintain urine flow during the hours when concentration naturally rises. The temporary inconvenience of nighttime bathroom trips is a worthwhile trade-off when you’re actively trying to pass a stone.