How Much Water Should I Drink Per Day?

You have probably heard you should drink 8 glasses of water a day. That number is easy to remember, but it is not actually based on strong science. Your real water needs depend on your body size, how active you are, the climate you live in, and what you eat. Here is what the research actually says.

The Quick Answer: A Better Rule of Thumb

A more evidence-based guideline than "8 glasses" is to drink half your body weight (in pounds) in ounces of water per day. A 160-pound person would aim for about 80 ounces (10 cups or 2.4 liters). A 200-pound person would aim for about 100 ounces (12.5 cups or 3 liters). This scales with body size, which the 8-glass rule does not.

Add 12 to 16 ounces for every 30 minutes of exercise, more in hot or humid weather. If you drink coffee or alcohol, which have mild diuretic effects, add a glass of water for each cup of coffee or alcoholic drink.

What the Science Says

The National Academies of Sciences, Engineering, and Medicine (NASEM) recommends a total daily water intake of about 3.7 liters (125 oz) for men and 2.7 liters (91 oz) for women. This includes water from all sources: drinking water, other beverages, and food. About 20% of your daily water intake typically comes from food, especially fruits and vegetables like cucumbers, watermelon, oranges, and lettuce.

That means the actual amount you need to drink (not counting food) is closer to 100 ounces for men and 73 ounces for women as a baseline. Active people, people in hot climates, and pregnant or breastfeeding women need more.

Daily Water Intake by Body Weight

Where the "8 Glasses" Rule Came From

The 8-glasses-a-day advice is commonly attributed to a 1945 report from the US Food and Nutrition Board, which recommended 2.5 liters of daily water intake for adults. However, the report also noted that most of this water would come from food, a detail that was widely overlooked. Over the decades, the simplified version became folk wisdom despite having no formal scientific backing as a universal guideline.

Signs You Are Not Drinking Enough

Thirst is the most obvious signal, but it is not always reliable, especially in older adults. Other signs of mild dehydration include dark yellow urine (pale straw color is ideal), dry mouth or lips, headaches, fatigue, difficulty concentrating, and dizziness when standing up quickly. If your urine is consistently dark, you need to drink more.

Can You Drink Too Much Water?

Yes, but it is rare in everyday life. A condition called hyponatremia occurs when you drink so much water that your blood sodium levels drop dangerously low. This is most common in endurance athletes who drink excessive amounts during long events without replacing electrolytes. For most people, the kidneys can handle up to about a liter per hour. The risk is not something most people need to worry about under normal circumstances.

Does Coffee Count as Water?

Yes, mostly. Coffee and tea contribute to your daily fluid intake. While caffeine has a mild diuretic effect, the water in coffee more than offsets it. A cup of coffee provides nearly the same hydration as a cup of water. That said, heavily sweetened coffee drinks add a lot of calories without much hydration benefit. If you are curious about how much caffeine you are consuming, check our Caffeine Calculator.

Practical Tips for Drinking More Water

Carry a water bottle. Having water within arm's reach makes it easy to sip throughout the day without thinking about it. Choose a bottle you like using and keep it filled.

Drink a glass first thing in the morning. You wake up mildly dehydrated after hours without water. Starting the day with a full glass sets a good baseline.

Eat your water. Fruits and vegetables like watermelon, cucumbers, strawberries, celery, and oranges are over 90% water. Soups and smoothies count too.

Set reminders if needed. If you forget to drink, set hourly reminders on your phone until the habit sticks. Most people find they no longer need reminders after a week or two.

Flavor it. If you find plain water boring, add lemon, cucumber, mint, or berries. Sparkling water counts too. Avoid water enhancers with added sugar or artificial sweeteners if you can.

Related Tools

Get your personalized target with the Water Intake Calculator, check your caffeine intake with the Caffeine Calculator, or find your daily calorie needs with the Calorie Calculator.