Participants were randomized into two groups. One received usual care and general advice about drinking enough fluids. The other joined a structured hydration program: smart water bottles that recorded intake, individual drinking goals, reminders, coaching, and small financial rewards. Daily fluid targets were calculated so that each participant would produce at least 2.5 liters of urine per day — the volume that stone guidelines generally target for people at risk of recurrence.
Researchers followed both groups for two years, and they did not rely only on self-reported drinking. They used medical imaging and other clinical information to determine whether new stones appeared or existing stones grew. That design matters: it measured the outcome stone patients actually care about — recurrence — rather than just the intermediate step of drinking more.
The hydration program did change behavior. People in the support group drank more fluids and produced more urine than those receiving usual care. The difference, however, was not large enough to produce a statistically significant reduction in kidney stone recurrence. In other words, the structured program moved the needle on intake but not on the outcome that counts.
The study does not say that water does not help prevent stones. Good hydration remains an important part of prevention, and some individual patients may still benefit from increasing fluid intake. What the trial shows is something more practical and more humbling: maintaining a large increase in daily fluid intake over years is genuinely hard, and even smart bottles, reminders, coaching, and rewards could not keep everyone consistently at the recommended urine target. Adherence is the bottleneck — not the concept.
If you have had a kidney stone, the practical reading of this trial is not "water doesn't matter." It is "the 2.5-liter urine target is the goal, and the hard part is hitting it every day." The measured version of the advice looks different now: instead of a vague "drink more," the working target is a specific urine volume, tracked with the signals you already have — pale, plentiful urine. And because adherence is the known weak point, the practical tools matter: a bottle you actually carry, a refill schedule tied to meals and breaks, and a way to notice when intake has slipped.
Researchers also note that prevention may need to become more personal. Fluid needs vary with body size, diet, physical activity, climate, and other health factors. Future strategies could combine individualized hydration goals with dietary changes or treatments that reduce the ability of minerals to form stones. For now, the individual version of that idea is simple: know your own target, and treat the water plan as something that needs a system, not a resolution.
Not all fluids carry the same oxalate column. The table below shows measured values for the common stone-table drinks.
| Food | Oxalate (mg) | Serving | Rating |
|---|---|---|---|
| Water | 0 | 1 cup | Safe |
| Milk, whole or low-fat | 0 | 1 cup | Safe |
| Lemonade, fresh | 2 | 1 cup | Safe |
| Apple juice, unsweetened | 1 | 1 cup | Safe |
| Cranberry juice | 3 | 1 cup | Safe |
| Soda, cola-type | 1 | 12 oz | Safe |
| Orange juice, fresh | 1 | 1 cup | Safe |
| Black tea | 10-15 | 1 cup | Safe |
| Green tea | 3-5 | 1 cup | Safe |
The trial's target — 2.5 liters of urine a day — is the practical number, and it translates to roughly 3 liters of total fluid for most adults, more in heat or with exercise. The system that makes it work is boring and reliable: a water bottle at every station (desk, car, bedside), a glass with each meal, and one refill between meals. The trial's honest lesson is that none of this is automatic — the people in the study had every tool and still fell short. That is not a reason to give up the bottle; it is a reason to make the bottle impossible to ignore.
No. The study tested whether extra support for drinking more water reduced recurrence over two years, and the support group did drink more and produce more urine — the reduction in recurrence just was not statistically significant. Hydration remains an important part of prevention; the trial's lesson is about adherence, not about water being useless.
The working target is a urine output of about 2.5 liters per day, which for most adults means roughly 3 liters of total fluid — more in hot weather or with exercise. Pale, plentiful urine is the day-to-day signal that you are on track.
Water is the base of the plan. Citrus drinks like lemonade add citrate, which can help inhibit crystal formation. Milk is a calcium-plus-fluid twofer. The drinks to portion are the sugary ones — the UK Biobank data links higher sugar-sweetened beverage intake to higher stone risk.
See how oxalate values are measured and verified on our data methodology page.