How Much Water Should You Drink a Day? What Health Bodies Say
There is no single number that fits everyone. The NHS suggests about 6 to 8 cups or glasses of fluid a day as a rough guide, while European and American scientific panels give higher figures for total water, because food supplies part of what the body takes in. Which figure applies to you depends on your size, activity, climate and health. This article lays out what the main bodies actually say and how to read it.
The numbers from three sources
Different organizations measure different things, which is why the figures look inconsistent.
| Source | What it measures | Figure |
|---|---|---|
| NHS (UK) | Fluids to drink | About 6 to 8 cups or glasses a day, described as “just a guide” |
| EFSA (EU, 2010) | Adequate water intake from drinks and food, for moderate temperature and activity | 2.0 liters for women, 2.5 liters for men |
| National Academies (US, 2004) | Adequate intake of total water, including food | About 2.7 liters for women, 3.7 liters for men |
The NHS figure is about drinks alone. The EFSA and National Academies figures count water from every source, including the moisture in fruit, vegetables, soup and other foods. The National Academies report that about 80 percent of people’s total water comes from drinking water and other beverages and about 20 percent from food. So a person who meets the American figure for total water would not need to drink that whole amount as plain water.
The National Academies also describe their numbers as adequate intakes for healthy, mostly sedentary people in temperate conditions, and they note that very active people or people in hot climates may need more. They add that thirst, together with the normal habit of drinking with meals, is enough for most healthy people to stay hydrated (National Academies; EFSA).
What counts toward your fluid intake
The NHS says water, lower-fat milk and lower-sugar drinks count, including tea and coffee. It advises children to avoid sugary fizzy drinks and juice drinks, and suggests limiting fruit juice and smoothies to one small glass (150 ml) a day, ideally with a meal (NHS).
Plain water has no sugar or calories, so it is a simple default, but it is not the only way to get fluid. Soups, fruit, vegetables and yogurt also contribute, which is part of why the scientific panels count food moisture in their totals.
Things that raise or lower your needs
The same NHS page says you may need more fluid if you are pregnant or breastfeeding, somewhere hot, very active for long periods, or ill. Other factors that commonly change needs:
- Body size. Body size affects how much water the body holds and turns over each day.
- Exercise. Sweat losses vary widely between people and between workouts.
- Heat and altitude. Both increase fluid loss through skin and breath.
- Diet. A diet heavy in fruit, vegetables and soups contributes more water than one that is mostly dry foods.
- Illness. Fever, vomiting and diarrhea cause rapid losses.
- Certain medicines or conditions. Some heart and kidney conditions call for limits on fluid, so general advice does not apply to everyone.
A practical check: urine color and thirst
The NHS suggests aiming for pee that is a clear pale yellow. Darker urine can mean you need more fluid, although some vitamins and foods also change its color. For most healthy adults, drinking when thirsty and with meals covers the day.
Can you drink too much?
Yes, though it is uncommon. Taking in more fluid than the body loses can dilute the sodium in the blood, a condition called hyponatremia. The Mayo Clinic lists drinking too much water as one cause and notes that long endurance events, where sweat loss is high, carry particular risk; it suggests that athletes drink only as much as they lose through sweat, with thirst a generally good guide (Mayo Clinic). For ordinary daily life, there is no reason to force down water beyond thirst.
People with kidney, heart or hormone-related conditions, and people taking certain medicines, can be more sensitive to both too little and too much fluid. That is one more reason a doctor, not a general rule, should set personal limits.
Where water quality fits in
Hydration advice assumes the water itself is safe. Public suppliers publish annual quality reports, and private wells are usually the owner’s responsibility to test. Our pages on pH and drinking water and drinking water in the news cover related questions about what is in tap water and how it is reported.
Frequently asked questions
Is 8 glasses a day a rule?
No. The NHS describes 6 to 8 cups or glasses as a guide, not a rule. Needs shift with age, activity, climate and health, and food supplies part of your water.
Does coffee or tea count?
According to the NHS, tea and coffee count toward fluid intake, particularly lower-sugar versions.
How much water should children drink?
Needs depend on age and size. The NHS advises that water and milk are the best drinks for children, and a pediatrician or national health service can give guidance for a particular child.
Should I drink more when I exercise?
Often yes, particularly in heat. Match intake to sweat and thirst, and ask a doctor about specific limits if you have a heart or kidney condition.
This article is general information, not medical advice. A doctor or registered dietitian can help with personal fluid needs, especially if you have a medical condition.