For how we live.
For most people eating normally, added electrolytes do little, and plain water rehydrates fine for ordinary exercise. The clearest endurance danger is drinking too much — and the proven use is illness, not the gym.
Plain fizzy water hydrates about as well as still water and is far less corrosive to teeth than juice or soft drinks. The cautions are narrow: flavoured versions and cola, not carbonation itself.
Mostly how concentrated it is: pale means well-hydrated, dark means less so. But a few colours — especially red or pink — are signals to get checked rather than to interpret at home.
Stones form when urine gets too concentrated. The best-tested defence is dull: drink enough that urine stays dilute. In one trial, that alone roughly halved recurrences.
For everyday exercise, food and water replace what sweat takes. The dangerous salt problem in endurance events is usually too much fluid, not too little sodium — and extra salt does not prevent it.
Two randomised trials found a 500 ml glass of water before meals adds a modest extra loss — about 1.3 kg over 12 weeks in one. The effect is real but small, short-term, and no substitute for the diet itself.
The familiar explanation — dehydration and lost salts — is the weakest part of the evidence. The better-supported idea is that cramping is a failure of nerve control, which is why a mouthful of pickle juice can stop one.
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.