For how we live.
Low fluid intake is a genuine, well-evidenced stone risk factor. Increasing fluid to produce plenty of urine is the single best-supported way to prevent another stone — better established than any diet tweak.
Observational studies link higher water intake to healthier kidneys. When a randomised trial coached people with kidney disease to drink more, their filtration fell at the same rate as the control group.
A 2002 review went hunting for the origin of "8 x 8" and found nothing. Two decades later, isotope measurements in 5,604 people put daily water use anywhere from about 1 litre to about 6.
Twenty-four firefighters completed a simulated fire scenario in full protective equipment. Electrolyte drinks beat plain water on several recovery measures, with one preserving jump power.
Researchers estimate about 58% of athletes are habitual low drinkers by a standard fluid-intake benchmark — and argue the field has barely studied what that means for long-term kidney and metabolic health.
Across 111 runners completing up to four trials each, two consumer devices tracked the direction of fluid loss reasonably well but missed the amount by 25% to 33% on average.
Seventy-two runners were sampled before and after the 2024 Boston Marathon. Every marker of kidney and intestinal injury rose, and staying hydrated did not change that.
Twenty adults sat for three hours at 39 °C with and without a fan, hydrated and not. Dehydrated, the fan raised heart rate and stopped feeling better, while sweat losses rose either way.