A good starting point is about 33 ml of water per kg of bodyweight a day (about 2.6 litres at 80 kg), plus more in the heat and on training days. Everything you drink counts, and pale yellow urine is the simplest sign you are drinking enough.
“Drink eight glasses a day” is easy to remember, but it was never based on much. A 60 kg office worker in an air-conditioned building and a 95 kg man training outdoors in a Gulf summer do not need the same amount.
How many litres is 8 glasses of water?
About 2 litres. A normal glass holds about 250 ml, so 8 glasses make 2,000 ml. It depends on the size of the glass:
- 200 ml glass: 1.6 litres
- 250 ml glass: 2 litres
- 300 ml glass: 2.4 litres
That is about right at 60 kg, but someone who weighs 80 kg needs more, about 2.6 litres.
A number that fits you
Rather than a flat eight glasses, a better starting point is about 33 ml per kilogram of bodyweight, then add more on hot days or hard training. Shulah’s water tool does this maths for you.
- 60 kg: about 2.0 litres a day
- 80 kg: about 2.6 litres a day
- 100 kg: about 3.3 litres a day
Then add roughly 0.25 to 0.8 litres depending on how active you are, and more again in the heat.
Everything you drink counts
Water is best, but it is not the only thing that counts. Laban, milk, tea and coffee all add to your total. Coffee and tea have a mild effect on the bladder, but for regular drinkers they still hydrate overall. Food counts too: watermelon, cucumber, oranges, soups and yoghurt are mostly water.
What does not help: sugary soft drinks and energy drinks. They add water, but also a lot of sugar and calories.
When you need more
- Heat and humidity. In summer you can lose a litre or more of sweat an hour while exercising outside.
- Training. Drink a glass or two in the two hours before, sip during, and drink after to replace what you lost. Weighing yourself before and after a long session shows how much: each kilo lost is about a litre of fluid.
- Illness with fever, vomiting or diarrhoea.
- Fasting. In Ramadan, spread your water between iftar and suhoor rather than drinking it all at once.
How to tell you are drinking enough
Thirst is a lagging signal, so sip through the day instead of chugging. Pale-yellow urine is the simplest real-time check that you’re on track.
- Pale yellow, like lemonade: well hydrated.
- Dark yellow or amber: drink more.
- Completely clear all day: you may be drinking more than you need.
Other signs you need water: headache, tiredness, dizziness and dry lips.
Drink steadily through the day, and let the colour, not a rule, tell you if it is enough.
Can you drink too much?
It is rare, but yes. Drinking many litres in a short time, especially during long endurance events, can dilute the salt in your blood. Spread your water out, and on very long sweaty days, include some salt from food or an electrolyte drink.
Make it a habit
- Keep a bottle where you can see it: on your desk, in the car.
- Have a glass with every meal and every prayer.
- Start your morning with a glass before coffee.
Sources
- European Food Safety Authority, reference values for water: EFSA, 2010
- How different drinks (tea, coffee, milk) hydrate: Maughan et al., 2016
- Moderate coffee drinking and hydration: Killer et al., 2014
The takeaway
Start from about 33 ml per kilo, add more for heat and training, count all your drinks, and check the colour. Shulah logs a glass, a bottle, coffee or tea in one tap, toward a daily goal set for your body, and its water widget lets you add 250 ml without opening the app.