How Much Water Do You Actually Need a Day?

"Eight glasses a day" is easy to remember, but it is a rule of thumb, not a scientific rule. The real answer depends on who you are, how active you are and what you eat. Here is what the National Academies say, and a simple way to check yourself.

Key takeaways

• The National Academies suggest about 91 ounces (2.7 liters) of total water a day for women and about 125 ounces (3.7 liters) for men.
• That total includes water from all drinks and from food.
• Pale yellow urine and not feeling very thirsty are simple signs you are on track.

The numbers

The National Academies set an adequate intake for total water, based on what healthy, well hydrated Americans actually take in:

1. Women: about 2.7 liters (91 ounces) a day.
2. Men: about 3.7 liters (125 ounces) a day.

This is total water. It comes from everything you drink and eat, not only from the tap. Food provides roughly a fifth of it in typical diets, mainly from fruit, vegetables and soup. The rest comes from drinks.

These are adequate intake figures, not a strict daily target. People who are very active or who live in hot places may need more.

What counts

• Water, plain or sparkling.
• Other drinks, including milk, tea and coffee. Caffeinated drinks still add to your fluids for most people. See how much caffeine is too much.
• Food, especially fruit, vegetables, yogurt and soup.

Sugary drinks count as fluid too, but they add sugar. Our guide to where added sugar hides shows the limits.

Five ways to know if you are drinking enough

1. Check your urine color. Pale yellow is a good sign. Dark yellow suggests you may need more.
2. Notice thirst. For most healthy people, drinking when you are thirsty works.
3. Look at your day. Heat, exercise, illness and fever all raise your needs.
4. Pair water with meals. A glass with each meal and snack covers a lot.
5. Carry a bottle. Having one nearby is the easiest habit to keep.

When to drink more, and when to ask a doctor

You may need more fluids when you exercise, spend time in the heat, or have a fever, vomiting or diarrhea. Pregnancy and breastfeeding also raise needs.

If you have a condition such as kidney disease or heart failure, your doctor may set a different fluid limit. Follow their advice, not a general number.

A quick example

Say you work at a desk, drink two cups of coffee, have water with lunch and dinner, and eat fruit and vegetables most days. You are probably close to your total without counting a single ounce. If you notice dark urine, headaches or tiredness on a busy day, add a glass or two and see how you feel.

Simple ways to drink more

• Keep a full glass by your desk and refill it at set times.
• Add lemon or cucumber if plain water bores you.
• Eat water rich foods like oranges, cucumber and soup.
• Link water to a habit: a glass after brushing your teeth and one before dinner.

Your checklist for this week

• ☐ Check your urine color a couple of times today.
• ☐ Pick a bottle or glass you will actually carry.
• ☐ Drink a glass with each meal.
• ☐ Add one water rich food to your day.
• ☐ Note when you feel thirsty and what helps.

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This is general information, not medical advice. Check with your doctor before major changes. If you have a condition that affects fluids, ask your care team.