aim for 30–35 ml of fluid per kilogram of body weight per day, counting tea, coffee, and the water in your food. On training days, add roughly 500–750 ml for every hour of exercise.Example: at 70 kg that's 2.1–2.4 liters a day, and about 2.6–3 liters on a day with an hour-long workout.
No fitness topic has collected more myths than water: eight glasses, "three liters no matter what," "coffee doesn't count." Let's sort out how much fluid your body actually needs, how workouts and heat change the number, and how to check your hydration in five seconds — no formulas or apps required.
01. Why hydration is worth tracking
An adult body is 50–60% water: it regulates temperature, carries nutrients to cells, lubricates joints, and maintains blood volume. When fluid runs low, all of that works worse — and sooner than you'd expect: losing just 2% of body weight through sweat already reduces endurance, strength, and focus.
The tricky part is that mild dehydration rarely feels like thirst. More often it disguises itself as fatigue, an evening headache, or sudden "hunger" that's really a request for a drink. That's why it pays to know your number instead of trusting your instincts on a busy day.
02. Calculate your target by body weight
The universal "two liters for everyone" ignores the most important variable — body size. The working guideline is 30–35 ml per kilogram of body weight per day:
- 60 kg — 1.8–2.1 L;
- 70 kg — 2.1–2.4 L;
- 80 kg — 2.4–2.8 L;
- 90 kg — 2.7–3.1 L.
Good news: all fluids count, not just plain water. Tea, coffee, soup, kefir, juicy vegetables and fruit — it all adds up, and roughly 20% of your fluid typically arrives with food. And yes, contrary to the myth, coffee doesn't "remove more than it gives": at normal doses, caffeine doesn't dehydrate you.
03. Adjustments: training, heat, illness
An hour of active training sweats out 0.5–1 liter on average — hence the extra 500–750 ml per hour of exercise. For precision, weigh yourself before and after a workout: the difference on the scale is almost entirely water, and it's worth replacing about one and a half times what you lost, since some of what you drink leaves as urine.
Your needs also rise in hot weather, in the dry air of a plane or a heated office, and when you're sick with a fever. On those days, just keep water in sight and drink more often than usual — exact milliliters matter less than regularity.
don't wait for strong thirst during a workout — take a few sips every 15–20 minutes, and drink 300–500 ml an hour or two before you start. That way you keep pace with your losses instead of chasing them.
04. How to check you're getting enough
The most honest indicator is free and always with you — urine color. Pale straw means hydration is on point; dark, closer to apple juice, means drink more; completely clear means you can ease off a little. Check during the day rather than first thing in the morning: the first morning sample is almost always concentrated.
Your second guide is plain thirst: in healthy people it's a reliable signal — don't ignore it, but don't fear the "if you're thirsty, it's already too late" line either. The one caveat is age: the sense of thirst dulls in older adults, so they're better off drinking on a schedule rather than waiting for the cue.
05. Myths: 8 glasses and "more is better"
"Eight glasses a day" isn't a law of nature — it's a rough half-century-old estimate: too much for some people, too little for others. Extra liters beyond your needs aren't a bonus either: surplus water doesn't "boost your metabolism" or flush out toxins — your kidneys and liver handle that just fine. And at the extreme, excess is dangerous: drinking a huge amount in a short time dilutes the sodium in your blood — a condition called hyponatremia, seen in marathon runners who drink far beyond their thirst. The simple conclusion: your target is individual, and "more" doesn't mean "healthier."
The bottom line
Work out your guideline — 30–35 ml per kilogram of body weight — remember that tea, coffee, and soup all count, and add 500–750 ml per hour of training. From there, two simple tools do the job: everyday thirst and urine color as your warning light. There's no magic in the liters — just the habit of keeping water within reach.
This material is for informational purposes and does not replace medical advice.
