Water and kidney stones: how much to drink

2026-10-30

If you've had a kidney stone, drinking more fluid is the single most effective thing you can do to prevent another one. The American Urological Association recommends drinking enough to produce at least 2.5 liters (about 85 fl oz) of urine a day. Because you also lose water through sweat and breathing, that usually means drinking somewhere around 2.5 to 3 liters a day, and more in hot weather or when you exercise. Your urologist may give you a different target depending on your stone type and health, so follow their advice first.

Why water prevents stones

Kidney stones form when minerals in urine — most often calcium and oxalate, sometimes uric acid or other substances — become so concentrated that they crystallize. The more urine you produce, the more diluted those minerals are, and the harder it is for crystals to form and grow.

That's not just theory. In a classic five-year trial, Borghi and colleagues (1996) followed 199 people after their first calcium stone. Half were told to drink enough to produce at least 2 liters of urine a day; the other half got no specific advice. After five years, stones had come back in 12 of 99 people in the high-water group versus 27 of 100 in the other group — roughly 12% compared with 27%. When stones did come back in the water group, they came back later.

This trial, together with observational data, is why urology guidelines put fluids first. The AUA guideline on medical management of kidney stones recommends that clinicians advise all stone formers to drink enough to reach a urine volume of at least 2.5 liters a day. The AUA published an updated version of this guideline in 2026, and a high urine volume remains the foundation of prevention.

How much to drink, in practice

Guidelines set a target for urine, not for drinking, because how much you need to drink depends on how much you lose in other ways. As a starting point:

The NHS advises adults who've had stones to drink 2.5 to 3 liters of water a day, and children 1 to 2 liters.
In hot weather, during exercise, or in physical jobs, you lose more through sweat and need to drink more to keep the same urine output.
The simplest check is color: your urine should be pale most of the day. Dark yellow urine means it's concentrated, which is exactly what you want to avoid. See what your urine color says about your hydration.

If you want to know your actual urine volume, ask your doctor about a 24-hour urine test. Besides volume, it measures calcium, oxalate, citrate, uric acid and sodium, which helps tailor your advice to the type of stone you form.

What 2.5–3 liters looks like

10 to 12 glasses of 250 ml (8 fl oz);
or five to six refills of a 500 ml (17 fl oz) bottle;
spread across the whole day, including the evening, so your urine doesn't get very concentrated for long stretches.

What to drink (and what to limit)

Water is the best choice. Other drinks count too, but some are better than others:

Coffee and tea count toward your total. The NHS advises avoiding lots of caffeinated drinks, so keep them moderate.
Lemon in water is a common tip, and the NHS mentions adding fresh lemon juice to water. Citrate in urine helps stop calcium crystals from forming, which is why some people are prescribed citrate; how much a squeeze of lemon adds on its own is less certain, but it can make water easier to drink.
Sugary soft drinks and lots of fizzy drinks are best limited. The NHS also advises against lots of alcohol.

If you're unsure which drinks count toward your fluid total, see do coffee, tea, milk and juice count toward your water goal?

Diet matters too

Fluids are the base, but diet changes can lower risk further. According to the NIDDK:

Limit salt. Sodium makes your kidneys pass more calcium into urine. NIDDK advises adults to aim for less than 2,300 mg of sodium a day; the NHS gives a limit of 6 g of salt.
Don't cut calcium. Calcium from food, in normal amounts, binds oxalate in your gut and can lower your risk. Cutting dairy without advice can backfire.
If you form calcium oxalate stones, your doctor may suggest limiting very high-oxalate foods such as spinach, rhubarb, nuts and wheat bran.
Moderate animal protein. A lot of meat, fish and eggs can raise the risk of some stone types.

What's right for you depends on your stone type, so don't change your diet drastically without talking to your doctor.

When fluid advice doesn't apply

Don't increase your intake to these levels without medical advice if you have heart failure, advanced kidney disease or any condition where your doctor limits fluids. Drinking very large volumes quickly is also unsafe; the kidneys can only excrete so much at once. See can you drink too much water?

Get medical help urgently if you have severe pain in your side or back, pain with fever or chills, blood in your urine, or you can't pass urine.

Making 3 liters a day realistic

The hard part of stone prevention isn't understanding it; it's drinking that much every single day, for years. A few things help:

Anchor glasses to routines: one on waking, one with each meal, one at each break.
Carry a bottle you know the size of, so you can count refills.
Drink more on hot days and after exercise.
Use reminders. Water Tracker suggests a goal based on your weight and activity, and you can adjust it to the amount your urologist recommends. Log a glass with one tap from your iPhone, Apple Watch or a widget; reminders stop once you've reached your goal; and charts show your average and streak, so you can see whether you're consistently hitting the target. Each drink can be saved to Apple Health, which is handy if you want to show your doctor your intake.

More ideas are in 15 easy ways to drink more water.

Bottom line

For people who've had a kidney stone, the goal is enough fluid to pass at least 2.5 liters of urine a day — usually 2.5 to 3 liters, mostly water. In the key trial, aiming for at least 2 liters of urine cut stone recurrence by more than half. Keep your urine pale, spread drinks through the day, limit salt, keep normal calcium, and ask your doctor about a 24-hour urine test to tailor the plan to your stone type.

This article is general information, not medical advice. If you have a health condition, are pregnant or take medication, ask your doctor how much you should drink.