How much water should you drink a day?

February 20, 2026

5 minutes

Healthy Eating

Most of us have heard the advice from experts: Drink eight 8-ounce glasses of water every day for optimal health (the "8x8 rule"). After all, the average adult's body is made up of 50 to 70 percent water. But is the 8x8 rule accurate, or is this an arbitrary number? Hint: It's an arbitrary number, and it doesn't apply to everyone.

The fact is that we all need plenty of water, but deciding how much water to drink in a day depends on several different factors. Let's dive in and learn more about precisely how much water you need—based on your unique situation—and why it's important to stay hydrated.

How much water should you drink daily?

You likely weren't surprised to learn that the 8x8 rule isn't the ideal fit for everyone. So, if it's not eight 8-ounce glasses of water per day, how much water should a person drink daily? It depends. While it's a simple question, the answer is complicated.

We do have a short answer to this question, but please keep reading to determine how much water you need based on your unique circumstances. According to the U.S. National Academies of Sciences, Engineering, and Medicine, this is how much water adult men and women should drink every day:

• Males: 15.5 cups (125 ounces or 3.7 liters) per day
• Females: 11.5 cups (91 ounces or 2.7 liters) per day

Note that these figures for adults are for total daily fluid intake. We also get up to 20 percent of our daily fluids from the foods we eat, especially if we eat plenty of water-rich fruit and vegetables. Milk, coffee, tea, and most other beverages also count toward this recommended fluid intake.

The recommended water intake for children is slightly different, per the Institute of Medicine of the National Academies. The ideal amount depends on activity levels and medical conditions. Generally, children should drink this much water every day:

• Children aged 4-8: 40 ounces
• Boys aged 9-13: 64-80 ounces
• Girls aged 9-13: 56-72 ounces
• Boys aged 14-18: 88-112 ounces
• Girls aged 14-18: 64-80 ounces

Other factors impacting recommended fluid intake

Several other factors determine how much water you actually need to drink every day:

• Geographical location: If you live in a hot, dry, or humid region, you need to drink more water. People who live in high-altitude areas such as mountains also need more water to stay adequately hydrated.
• Environment: Spending time outdoors or working in overheated rooms may increase your water intake needs.
• Diet: People who drink a lot of caffeinated beverages may lose more water because of frequent urination. Equally important, you'll probably need more water if you eat a diet high in spicy, salty, or sugary foods.
• Season or outdoor temperature: Most people require more water during the warmer months because of perspiration, especially individuals who spend time outdoors.
• Overall health: Illnesses and medical conditions affect how much water you need. For example, when you have a fever or infection, you may lose more fluids through diarrhea and vomiting. Health conditions like diabetes also increase your hydration needs.
• Activity levels: If you're active or stand and walk more than average, you probably need more water than someone with a desk job. Also, if you do physical activities such as exercising or even just getting your steps in, you'll need to recover your water loss by drinking more.
• Pregnancy or breastfeeding: People who are pregnant or breastfeeding need more water to keep themselves hydrated.

To calculate precisely how much water you need to drink every day, use this tool from the University of Missouri.

Benefits of drinking water throughout the day

Every single cell, tissue, and vital organ in your body requires water to function properly. Here are some of the many reasons to make sure you drink plenty of water:

• Heart health: Maintaining adequate hydration contributes to heart health and reduces the risk of cardiovascular failure.
• Brain health: Your brain is made up of about 73 percent water, and the lubrication helps with firing your hormones and neurotransmitters. Hydration has an effect on focus and concentration, but it also plays a role in your moods, memory, and emotional health.
• Weight maintenance: Drinking more water can curb your appetite and increase your metabolism.
• Kidney health: Your kidneys use water to remove waste and toxins from the body. Kidneys also play a crucial role in maintaining the right balance of salt, water, and minerals in your body.
• Joint health: Joint cartilage is made up of about 80 percent water, so staying well-hydrated can help lubricate and cushion your joints.
• Energy levels: Poor hydration affects the flow of nutrients to our cells, resulting in fatigue. Stay well-hydrated to keep your energy level high.
• Immune system health: Staying hydrated helps us have a more robust immune system, which fights off diseases and illnesses.
• Skin health: Our skin consists of about 64 percent water. If your skin has to give up moisture to more critical bodily functions, it will become dry. This can eventually result in wrinkles and irritation.

What happens if you don’t drink enough water?

Staying adequately hydrated has a positive impact on nearly every aspect of your health. Not drinking enough water has an effect on your physical performance and can cause cognitive impairment, kidney and urinary problems, and an increased risk of various other health issues. Moreover, severe dehydration requires immediate care because it's a medical emergency.

You may be approaching dehydration if you're feeling lightheaded or overly tired and have a dry mouth. Signs of severe dehydration include:

• Dark urine: Aim for pale yellow urine. If your urine is the color of dark apple cider, you're likely dehydrated unless you are taking medication that changes the color of your urine.
• Extreme thirst: If you're feeling thirsty, you may already be approaching dehydration. But don't rely completely on thirst. Note that people aged 65 and older are at increased risk of dehydration because the body's thirst mechanisms begin to malfunction with aging. Newborns and infants also face a higher risk of dehydration because of their low body weight.

Can you drink too much water?

Most adults rarely drink too much water, but athletes such as marathon runners need to be careful about drinking too much as they attempt to prevent dehydration. If you drink too much water, your kidneys can't eliminate the excess water, causing your blood's sodium content to become diluted. The result can be a potentially fatal condition called hyponatremia. According to the National Kidney Foundation, life-threatening overhydration symptoms include:

• Confusion, headache, or fatigue
• Low blood pressure
• Nausea or vomiting
• Energy loss
• Muscle weakness
• Cramps or twitching
• Restlessness
• Seizures or coma

Staying hydrated for optimal health

How much water should you drink a day? We've laid out all of the different factors that affect how much H2O you should have every day, along with the most important water benefits. The answer is that it's different for everyone. Understanding your personal needs is the first step.

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