Plain carbonated water is not bad for kidney stones. The carbonation itself, which is simply dissolved carbon dioxide, does not increase your risk of forming stones or make existing stones worse. The confusion comes from lumping all fizzy drinks together. Cola and other sugar-sweetened sodas do raise kidney stone risk, but the culprits are phosphoric acid, fructose, and excess sodium, not the bubbles.
Why Cola Gets Confused With Sparkling Water
A large study published in the Clinical Journal of the American Society of Nephrology found that higher consumption of sugar-sweetened soda was associated with a higher incidence of kidney stones. In a separate randomized trial among men with a history of stones, those who continued drinking soft drinks containing phosphoric acid had more stone recurrences than those who switched to beverages acidified with citric acid. Cola specifically can produce urinary changes that promote calcium oxalate stone formation, the most common stone type.
Noncola carbonated beverages told a completely different story. In research tracking kidney disease risk, noncola carbonated drinks showed no increased risk at all. The key difference: cola is acidified with phosphoric acid, while most other carbonated beverages use citric acid. Phosphoric acid increases phosphorus levels in the body and alters urine composition in ways that favor stone formation. Citric acid, by contrast, is actually protective.
How Sparkling Water Can Actually Help
Staying well hydrated is the single most effective way to prevent kidney stones, and sparkling water hydrates just as well as still water. The goal is to produce at least 2.5 liters of urine per day, which typically means drinking about 3 liters of fluid. If carbonation makes you more likely to hit that target because you enjoy it more than flat water, it’s working in your favor.
Some sparkling mineral waters offer an additional benefit. Those with meaningful bicarbonate content can raise urinary pH and increase citrate excretion, both of which inhibit stone formation. Research has shown that bicarbonate-rich mineral water can even serve as a partial replacement for potassium citrate, a medication commonly prescribed to prevent recurrent stones. Not all sparkling waters contain bicarbonate, though. Check the label for bicarbonate or “HCO3” content if this matters to you.
Calcium and Magnesium in Mineral Water
It might seem counterintuitive, but calcium in your water and food actually reduces kidney stone risk rather than increasing it. When you consume calcium with meals, it binds to oxalate in your intestines and forms an insoluble compound that passes through your digestive tract instead of being absorbed into your bloodstream and filtered through your kidneys. Less oxalate reaching the kidneys means fewer calcium oxalate stones.
Mineral waters vary widely in their calcium and magnesium content. Some brands contain very little, while others deliver a significant portion of your daily needs per liter. Magnesium also appears to have a protective effect. The variability is worth noting: commercially available bottled water sometimes lacks these protective minerals or contains imbalanced ratios that may reduce the benefit. If you’re choosing a sparkling mineral water partly for stone prevention, look for one with higher calcium and magnesium on the nutrition label.
Watch Out for Additives and Flavoring
Plain seltzer is just water and CO2. Club soda, however, contains added sodium. Excess sodium in your diet pushes more calcium into your urine, and since the most common kidney stones form with calcium, that’s a problem. If you drink multiple cans of club soda a day, the sodium adds up. Seltzer or plain sparkling mineral water is a better choice.
Flavored sparkling waters are mostly fine, but read the ingredients. The most commonly added acids in flavored beverages are citric acid, phosphoric acid, and malic acid, in that order of frequency. Citric acid (found in citrus-flavored varieties) is not a concern and may even be mildly beneficial. Phosphoric acid is the one to avoid, and it’s primarily found in cola products rather than flavored sparkling waters. Still, it’s worth a quick glance at the label to confirm.
Tonic water deserves its own warning. Despite its association with sparkling water, tonic water is a sugar-sweetened beverage. Fructose increases the urinary excretion of calcium, oxalate, and uric acid, all of which raise stone risk. If you’re prone to stones, treat tonic water more like soda than like sparkling water.
A Simple Guide for Stone-Prone Drinkers
- Plain seltzer or sparkling water: Safe. Hydrates as well as still water and carries no stone risk from carbonation alone.
- Sparkling mineral water (bicarbonate-rich): Potentially beneficial. Can raise urinary pH and citrate levels, both of which inhibit stone formation.
- Club soda: Use in moderation. The added sodium can increase urinary calcium excretion over time.
- Flavored sparkling water (unsweetened): Generally safe. Avoid any containing phosphoric acid, though this is uncommon outside of colas.
- Tonic water: Treat as a sugary drink. The fructose content promotes stone formation.
- Cola and sugar-sweetened soda: The real problem. Phosphoric acid and fructose both independently raise stone risk, and drinking two or more colas per day is associated with increased kidney disease risk.
The bottom line is straightforward: the bubbles aren’t the issue. What’s dissolved alongside those bubbles, whether it’s phosphoric acid, sugar, or sodium, determines whether a carbonated drink helps or hurts your kidneys. Plain sparkling water is a perfectly good way to stay hydrated and keep stones at bay.