Staying Hydrated: How Much Water Do You Really Need?

Water makes up a large share of your body weight and is involved in almost everything your body does — regulating temperature, cushioning joints, protecting tissues, and helping remove waste. Even mild dehydration can leave you feeling tired, unfocused, or headachy.

You've probably heard you should drink "eight glasses a day." It's an easy-to-remember goal, but actual needs vary from person to person. Here's what the evidence-based guidance says and how to tell whether you're getting enough.

How much water do you need?

The National Academies of Sciences, Engineering, and Medicine have set general reference amounts for total daily water intake — which includes water from all beverages and food — of about:

• About 15.5 cups (3.7 liters) a day for men
• About 11.5 cups (2.7 liters) a day for women

That may sound like a lot, but roughly 20% of daily water typically comes from food, especially fruits, vegetables, soups, and dairy. The rest comes from drinks of all kinds.

These are general reference values, not strict targets. Many healthy people meet their needs by drinking when they're thirsty and with meals.

What affects your fluid needs?

You may need more fluid when:

• You're physically active, especially for long periods or at high intensity
• It's hot or humid, or you're at high altitude
• You have a fever, vomiting, or diarrhea
• You're pregnant or breastfeeding

On the other hand, people with certain health conditions — such as heart failure or some kidney diseases — may be told to limit fluids. Always follow your doctor's guidance if you have a medical condition.

Signs you might be dehydrated

According to MedlinePlus, common signs of dehydration in adults include:

• Feeling very thirsty
• Dry mouth
• Urinating less often, or dark-colored urine
• Fatigue
• Dizziness or lightheadedness
• Headache

Older adults may not feel thirsty as readily, which makes them more vulnerable to dehydration. If you care for an older family member, encourage regular drinks throughout the day. Our guide on healthy eating after 60 covers this in more detail.

A simple hydration check

One easy way to gauge your hydration is to look at your urine. Pale yellow usually means you're well hydrated. Dark yellow or amber can be a sign you need more fluids. (Some vitamins and medications can change urine color, so this isn't a perfect test.)

What counts toward hydration?

• Water is the best choice: it has no calories, no added sugars, and it's inexpensive from the tap.
• Milk and fortified soy milk provide fluid plus calcium, protein, and vitamin D.
• Unsweetened tea and coffee count toward your fluid intake. Moderate caffeine doesn't cause meaningful dehydration for most people, though too much caffeine late in the day can affect sleep — see our guide on screens, caffeine, and sleep.
• Water-rich foods like cucumbers, watermelon, oranges, lettuce, and soups add to your total.

Drinks to limit:

• Sugary drinks such as regular soda, sweetened tea, and many sports and energy drinks. These are a leading source of added sugars in the U.S. diet.
• Alcohol, which can increase fluid loss and adds calories.

Do you need sports drinks?

For most everyday exercise, water is enough. Sports drinks may be useful during long, intense exercise in the heat, when you're losing a lot of sweat. For a typical 30-minute walk or workout, they mostly add sugar and calories.

10 easy ways to drink more water

1. Carry a reusable water bottle and refill it throughout the day.
2. Drink a glass of water with every meal.
3. Start your morning with water before coffee. It fits nicely into a healthy morning routine.
4. Add natural flavor with lemon, lime, cucumber, mint, or berries.
5. Try sparkling water if you miss the fizz of soda.
6. Set reminders on your phone if you tend to forget.
7. Eat more fruits and vegetables, which are naturally water-rich.
8. Drink before, during, and after exercise.
9. Keep water visible on your desk or kitchen counter.
10. Swap one sugary drink a day for water, and build from there.

Can you drink too much water?

It's uncommon, but drinking extremely large amounts of water in a short time can lower blood sodium to dangerous levels, a condition called hyponatremia. This is mostly a concern for endurance athletes or in certain medical situations. For most people, drinking to thirst and with meals is safe.

The bottom line

There's no single water target that fits everyone. Drink regularly throughout the day, let thirst guide you, watch for darker urine as a sign you need more, and choose water over sugary drinks. If you have a health condition that affects fluid balance, follow your doctor's advice.