"Drink eight glasses of water a day" is probably the most repeated health tip in the world. But where did it come from, and is it true? The honest answer is that there is no single number that fits everyone. How much you need depends on your body, your activity, the weather and what you eat.
This guide looks at what health organisations actually say, what affects your needs and simple ways to build a hydration habit that works for you. It is general information, not medical advice.
Where the eight glasses rule came from
The "eight glasses" rule has no precise scientific origin, though it is roughly in line with what many people drink in total. Eight 8-ounce glasses is about 1.9 litres, or just under two litres. It is easy to remember, which is probably why it stuck. It is a decent ballpark for some people, but it is not a rule, and it ignores the water you get from food and other drinks.
What health bodies say
A widely cited set of reference values comes from the US National Academies of Sciences, Engineering, and Medicine. They suggest an adequate total water intake of about 3.7 litres a day for adult men and about 2.7 litres a day for adult women. Importantly, this is total water from all sources, including food. Around 20 percent typically comes from food, such as fruit, vegetables and soups, so the amount you need to drink as beverages is roughly 3.0 litres for men and 2.2 litres for women.
The same guidance suggests higher totals during pregnancy, about 3.0 litres, and while breastfeeding, about 3.8 litres. Other countries and organisations publish slightly different figures, which is a reminder that these are guidelines for groups of people and not exact prescriptions for you.
What changes your needs
- Heat and humidity. You lose more water through sweat in warm weather, so your needs rise.
- Exercise. The longer and harder you work out, the more you lose. Add fluid before, during and after.
- Body size. Larger bodies generally need more water than smaller ones.
- Altitude. Higher altitudes can increase fluid loss through faster breathing and drier air.
- Diet. A diet rich in fruit and vegetables gives you more water from food. Salty or high-protein meals can make you feel thirstier.
- Illness. Fever, vomiting and diarrhoea cause extra fluid loss. If you are unwell, follow the advice of a doctor.
- Medical conditions and medicines. Some conditions and medications change how much fluid you should drink. If you have kidney, heart or other health conditions, ask your healthcare provider for personal guidance.
Signs you are well hydrated
Instead of counting every millilitre, many people find it easier to watch simple signals:
- Your urine is pale yellow, like light straw, rather than dark amber.
- You do not feel thirsty much of the time, and your mouth is not dry.
- You have steady energy and can concentrate comfortably.
- You are going to the toilet regularly during the day.
Signs of mild dehydration can include thirst, a dry mouth, headaches, tiredness and dark urine. Severe dehydration, with dizziness, confusion, a very dry mouth, a rapid heartbeat or little to no urine, needs urgent medical attention.
Can you drink too much?
It is rare, but possible. Drinking extreme amounts of water in a short time can dilute the sodium in your blood, a condition called hyponatremia. It has been reported mostly in endurance events and in people who force themselves to drink far beyond thirst. For most healthy people, drinking to thirst and to the colour of urine is a sensible approach. Do not try to flush your body with huge volumes of water.
Does coffee or tea count?
Yes. Caffeinated drinks contribute to your fluid intake. Although caffeine has a mild diuretic effect, research suggests that moderate amounts of coffee and tea hydrate you about as well as water in people who are used to caffeine. Water is still an excellent default, especially since it has no sugar or calories, and you can learn more about caffeine in our caffeine guide.
Easy ways to drink more
- Keep a bottle in sight. Visible water is far more likely to be drunk.
- Attach it to routines. Have a glass when you wake up, with each meal and when you get home.
- Add flavour naturally. A slice of lemon, cucumber, mint or berries can make plain water more appealing.
- Eat your water. Watermelon, oranges, cucumbers, tomatoes and soups all contribute.
- Use reminders. A phone alarm, a marked bottle or a habit tracker can help until the habit is automatic.
- Start before you are thirsty. Thirst is a signal that you are already a little behind, especially when you are active.
Spread it through the day
Sipping steadily is more comfortable than drinking a large amount at once. Many people drink most of their water in the morning and afternoon and taper off in the evening to avoid waking at night. If you find that you are waking often to use the toilet, try front-loading your intake earlier in the day.
Track your progress
Tracking is helpful because it turns a vague goal into something visible. The Daily Water Intake Tracker on LoveBloom lets you log your drinks through the day so you can see how close you are to your target. Remember that the target is a guide, not a test. If you want to build other healthy habits too, our guide to sleep and skincare routines shows how small daily choices add up.
The best hydration plan is the one you will follow: a bottle you like, a routine that fits your day, and a willingness to listen to your body.
This article is general information and not medical advice. Speak to a healthcare professional about your personal fluid needs, especially if you have a medical condition.