Drink like it
actually matters.
Most "8 glasses a day" advice is a guess. Hydration computes your real target from body weight, activity, climate and more, then helps you hit it with a live fill you can watch rise all day.
How much water do you actually need?
The "eight glasses" rule ignores that a 55 kg office worker in a mild climate and a 95 kg roofer in Arizona summer are not the same problem. Move the sliders. Your number updates live.
About 20% of your daily water comes from food (fruit, vegetables, soup, yogurt). The number above is total fluid intake. Roughly four fifths of it should come from what you drink.
How this number is built
No single formula fits everyone, so this estimator layers the factors that genuinely move fluid needs, in the same order a sports dietitian would consider them.
We start at roughly 33 ml per kilogram of body weight, a widely used baseline that scales with your size rather than assuming an average adult.
Exercise drives sweat loss, so we add a fixed amount per activity tier, from sedentary up to athlete-level training.
The running total is then scaled by climate, since heat and humidity can swing sweat loss dramatically.
Small adjustments reflect that men carry more lean tissue and water on average, and that older adults benefit from a slight nudge upward.
Altitude, heavy caffeine, alcohol, pregnancy, breastfeeding and illness each add a defined amount on top, reflecting their real fluid cost.
Treat the result as a smart starting point, then let urine colour and thirst fine-tune it. Your body is the final authority.
Fill the glass. Watch it rise.
Tap a drink to log it. The glass fills, the day's total climbs, and a week of progress builds underneath. Everything is saved on this device, so closing the tab keeps your day.
When to drink, hour by hour.
Hitting your target is less about volume and more about rhythm. Here is a simple, flexible template for spreading fluid across a typical waking day.
Water alone can leave you flat.
When you sweat hard or drink huge volumes of plain water, you lose and dilute electrolytes. The right pinch of sodium, potassium and magnesium is what actually keeps fluid where your body needs it.
DIY electrolyte mix
A homemade oral rehydration drink for hot days and hard workouts. Set your bottle size, get the recipe.
This is a general endurance-style mix. It is not a medical oral rehydration solution (ORS). For diarrhoea, vomiting or treating a sick child, use a pharmacy ORS sachet, which has clinically precise ratios.
Measure your sweat rate.
Weigh yourself before and after a workout (same scale, minimal clothing). The change, adjusted for what you drank, reveals how fast you lose fluid, so you can replace it precisely on race day.
Not every drink hydrates the same.
The Beverage Hydration Index compares how much fluid a drink retains versus still water (water = 1.00). Higher means it keeps you hydrated longer. Sort the table, or expand any card below for the full picture.
| Drink | Hydration index | Sodium | Sugar | Caffeine | kcal |
|---|
Yes, coffee counts. The old "coffee dehydrates you" claim is a myth at normal intake. A moderate caffeinated drink still hydrates you net positive. Per 100 ml values shown; figures are typical averages and vary by brand.
About a fifth of your water comes from food.
Water-rich foods hydrate you and deliver potassium, fibre and vitamins at the same time. These are sorted by water content. The juiciest are near the top.
| Food | Water content | Potassium | Why it helps |
|---|
What water actually does in you.
Nine plain-language deep dives into the physiology of hydration. Tap any card to expand it. No jargon left unexplained.
What water does for each part of you.
Hydration is not one benefit, it is dozens, spread across every system in the body. Tap a card to see how water keeps each one running.
The things that drain or save your water.
Heat, caffeine, altitude, salt and more all push your fluid balance around. Tap a card to see how each one works and what to do about it.
Where your water comes from.
Tap, filtered, bottled, mineral, spring. They differ in cost, taste and footprint more than in how they hydrate you. Tap a card for the honest comparison.
Hydration changes across a life.
A toddler, a marathoner, a pregnant woman and an 80 year old all have different fluid stories. Tap a card for what matters most at each stage.
The warning signs, decoded.
Your body signals dehydration long before you collapse. The clearest everyday gauge is the colour chart below. The cards show what each stage feels like, and why overhydration is its own danger.
The urine colour chart
The single most practical hydration check. Aim for pale straw, levels 1 to 3.
What you have heard versus what is true.
Hydration is buried under marketing and old wives' tales. Here are the most common myths, each paired with what the evidence actually says.
Small habits that actually stick.
You will not hit your target through willpower. You hit it by building water into things you already do. Here are the cues that work.
A plan for the day you are having.
Hydration is easy in theory and messy in real life. Here are practical playbooks for the situations that actually trip people up. Tap any card.
The mistakes that trip people up.
Most hydration failures are not dramatic, they are small habits that quietly leave you short or, occasionally, push you too far. Here are the usual suspects.
The whole thing on one card.
If you remember nothing else from this page, remember these. The fast rules of hydration, distilled.
Hydration, answered.
The questions people actually ask, with answers grounded in current sports-science and nutrition consensus.
The glossary.
Every term used on this page, defined in one breath.
Grounded in real guidance.
The figures and advice on this page reflect mainstream nutrition and sports-science consensus. These are the kinds of authoritative bodies that set it. Always defer to your own clinician for personal medical advice.