Researchers looked at drinking habits of over 10,000 American adults to understand how different types of water affect kidney stone risk. They found that people who drank more tap water had about 32% fewer kidney stones compared to those who drank less tap water. Bottled water didn’t show the same protective effect. The study suggests that tap water’s natural mineral content or other properties might help protect your kidneys from forming painful stones. While this is promising news, experts say more research is needed to fully understand why tap water appears to be better for kidney health than bottled water.

The Quick Take

  • What they studied: Whether the type of water people drink (tap versus bottled) affects their chances of developing kidney stones
  • Who participated: 10,246 American adults aged 20 and older who participated in a national health survey between 2009 and 2016. The group included people of different ages, races, weights, and health conditions.
  • Key finding: People who drank more tap water had 32% lower odds of getting kidney stones. Bottled water showed no significant protective or harmful effect. The relationship was consistent and linear—more tap water meant lower kidney stone risk.
  • What it means for you: Choosing tap water over bottled water may help reduce your kidney stone risk, though this is one study and more research is needed. This is especially relevant if you have a family history of kidney stones or have had them before. However, this doesn’t mean bottled water is harmful—it just didn’t show the same protective benefit in this study.

The Research Details

This was a cross-sectional study, which means researchers took a snapshot of people’s water drinking habits and kidney stone history at one point in time, rather than following people over many years. The researchers used data from the National Health and Nutrition Examination Survey (NHANES), a large government health study that tracks American health patterns.

Participants reported what they drank over 24 hours and whether they had ever been diagnosed with kidney stones. The researchers then used statistical methods to compare tap water drinkers with bottled water drinkers while accounting for other factors that might affect kidney stone risk, like age, weight, exercise, calcium intake, smoking, and existing health conditions like diabetes.

To make sure their findings were solid, the researchers used several different statistical approaches, including special matching techniques to create comparable groups and tests to check if the relationship between water type and kidney stones was straightforward or more complex.

Understanding which type of water might protect against kidney stones is important because kidney stones are painful and common—affecting millions of Americans. If tap water truly offers protection, it’s an easy, inexpensive change people could make. This research approach is valuable because it looks at real-world behavior in a large, diverse population rather than a small lab study.

Strengths: Large sample size of over 10,000 people, diverse population, adjusted for many confounding factors, multiple statistical methods used to verify findings. Limitations: Self-reported data (people’s memory of what they drank and whether they had stones), cross-sectional design (can’t prove cause-and-effect), single 24-hour dietary recall may not represent typical drinking habits, no information about water quality differences between regions.

What the Results Show

The main finding was that higher tap water intake was significantly associated with lower kidney stone risk. Specifically, people with higher tap water consumption had 32% lower odds of having kidney stones compared to those with lower intake. This relationship was consistent and linear, meaning more tap water was associated with progressively lower risk.

In contrast, bottled water intake showed no significant relationship with kidney stone risk—neither protective nor harmful. This was surprising to researchers because both tap and bottled water contain fluids that should help prevent stones.

When researchers grouped people by their overall water drinking patterns, they found that the combination of high tap water intake plus low bottled water intake was most protective against kidney stones. This suggests that tap water may have specific properties that bottled water lacks.

The researchers tested whether the relationship between tap water and kidney stones might be curved or complex rather than straightforward. They found it was actually linear—a simple, direct relationship. They also performed additional analyses to ensure their findings held true even when they adjusted for bottled water intake and looked at different subgroups of people (by age, sex, race, weight status). The protective effect remained consistent across these different groups.

Previous research has shown that overall fluid intake helps prevent kidney stones by diluting urine. However, this is one of the first studies to specifically compare tap water versus bottled water. The findings suggest that the type of water matters, not just the amount. Tap water typically contains minerals like calcium and magnesium, while bottled water varies widely depending on the source and processing. This study suggests those minerals in tap water might play a protective role.

This study has several important limitations. First, it’s cross-sectional, so it shows an association but cannot prove that tap water actually prevents kidney stones—people who drink tap water might differ in other ways. Second, kidney stone history was self-reported from memory, which can be inaccurate. Third, water intake was measured from just one 24-hour period, which may not reflect typical habits. Fourth, the study didn’t account for regional differences in tap water quality or mineral content. Finally, the study couldn’t explain the mechanism—why tap water appears protective remains unclear.

The Bottom Line

Based on this research, choosing tap water as your primary drinking water may help reduce kidney stone risk (moderate confidence level). This is especially worth considering if you have a personal or family history of kidney stones. However, this single study is not definitive proof, and more research is needed. General hydration remains important regardless of water type.

This is most relevant for people with a history of kidney stones, those with family members who’ve had kidney stones, and people at higher risk (men, people over 40, those with certain medical conditions). The findings may also interest public health officials considering water recommendations. People without kidney stone risk factors don’t need to change their habits based on this one study.

If tap water does offer protection, the benefit would likely build over months to years of consistent consumption, not days or weeks. Kidney stone formation is a gradual process, so prevention is a long-term strategy. If you have a history of stones, discuss hydration strategies with your doctor.

Want to Apply This Research?

  • Track daily tap water intake in ounces or cups alongside any kidney stone symptoms or concerns. Set a daily goal (typically 8-10 cups) and monitor consistency over weeks and months.
  • Replace bottled water purchases with a reusable water bottle filled with tap water. Set reminders to drink water throughout the day. Track the switch and monitor how you feel over time.
  • Log weekly tap water consumption averages and any kidney-related symptoms or concerns. Over months, look for patterns between higher water intake weeks and symptom reduction. Share data with your healthcare provider.

This research shows an association between tap water consumption and lower kidney stone risk, but cannot prove cause-and-effect. These findings are from one cross-sectional study and should not replace medical advice from your doctor. If you have a history of kidney stones, are at risk for kidney stones, or have kidney disease, consult your healthcare provider before making significant changes to your water intake or hydration habits. Individual water needs vary based on health conditions, medications, climate, and activity level. This information is for educational purposes only and is not medical advice.