Staying hydrated is crucial for your health. Water makes up about 60% of your body weight, and you lose water every day through sweat, urine, breathing and other bodily functions. Not drinking enough water can lead to dehydration, which causes symptoms like fatigue, dizziness and confusion. So how much water should you drink each day?
Quick answer
The general recommendation is to drink around 8 glasses or 64 ounces (oz) of water per day for women and 16 glasses or 128 oz per day for men. However, water needs can vary based on factors like age, gender, activity level and climate.
How much water do you need?
Your daily water needs depend on many factors:
- Age – Older adults need to drink more water because thirst signals become less effective with age.
- Gender – Men need more water than women because they have more muscle and a higher metabolism.
- Activity level – The more active you are, the more water your body needs to regulate temperature and replace lost fluids.
- Climate and environment – Hot, humid weather and high altitudes increase water loss through sweat.
- Health conditions – Problems like diabetes or kidney disease can affect hydration needs.
- Pregnancy and breastfeeding – Pregnant and nursing mothers need extra fluids to support blood volume and milk production.
As a baseline, the Institute of Medicine recommends the following daily water intakes:
| Group | Total Water (L/day) | Total Water (oz/day) |
|---|---|---|
| Infant 0-6 months | 0.7 | 24 |
| Infant 7-12 months | 0.8 | 27 |
| Children 1-3 years | 1.3 | 44 |
| Children 4-8 years | 1.7 | 58 |
| Girls 9-13 years | 2.1 | 71 |
| Boys 9-13 years | 2.4 | 81 |
| Girls 14-18 years | 2.3 | 78 |
| Boys 14-18 years | 3.3 | 112 |
| Adult females | 2.7 | 91 |
| Adult males | 3.7 | 125 |
As you can see, adult men generally need more water per day than adult women. The table also shows water needs increasing with age during childhood.
Factors that affect water needs
Age
Infants and children have higher water requirements per unit of body weight compared to adults. This is because children have a higher surface area to body mass ratio and higher metabolism.
As we age, our ability to conserve water decreases. Thirst signals become less effective, so older adults are at higher risk of dehydration. Seniors should be sure to drink regularly even when not thirsty.
Gender
Due to differences in body composition, males generally need more water than females each day. Men have less body fat and more lean muscle mass, so they produce more metabolic water. Hormonal differences also play a role.
Activity level
Physically active individuals need extra water to replace fluids lost through sweat. Athletes and people who exercise daily require more hydration than sedentary folks. Intense exercise and endurance sports like marathon running greatly increase water needs.
Heat and humid weather also make the body sweat more, so outdoor workers and athletes require additional fluids in hot environments.
Climate and altitude
Living in a hot or humid climate increases water loss through perspiration. At higher altitudes, the air is dryer so more water evaporates from the skin and lungs.
People living in desert regions or at high altitude need to drink more water to make up for increased respiratory and evaporative losses. The increased UV exposure at higher elevations can also raise fluid requirements.
Health conditions
Certain medical conditions affect hydration needs. Diabetes insipidus, a disorder that causes excessive urination, greatly increases daily water needs. Health issues like diabetes mellitus and kidney disease also require staying well-hydrated.
Pregnant and breastfeeding women need extra fluids to support increased blood volume and milk production. Water needs also rise during illnesses like diarrhea, vomiting or fever that deplete fluids.
Water intake recommendations
General guidelines recommend drinking around 8 x 8 ounce glasses of water per day, or 64 ounces total, for women. Men should aim for around 16 x 8 ounce glasses, or 128 ounces per day.
However, some groups suggest higher intakes. For example, the Institute of Medicine recommends 2.7 liters (91 oz) of total water intake per day for adult women and 3.7 liters (125 oz) for men. The European Food Safety Authority advises 2 liters (68 oz) for women and 2.5 liters (85 oz) for men.
Typical water intake ranges
While recommendations provide a goal, actual water intake can vary widely:
- Women: Common intakes range from 49-112 oz (1.5-3.4 liters) per day.
- Men: Intakes range from 64-156 oz (1.9-4.7 liters) daily.
Water intake is often inadequate during colder months when thirst drives are lower. Surveys show many people fail to meet recommendations and may be chronically underhydrated.
Does the 8 by 8 rule work?
Drinking eight 8-ounce glasses of water a day equals 64 ounces total, which meets the minimum intake for women set by the Institute of Medicine. However, men and other groups may need more than the “8 by 8” rule provides.
This rule is easy to remember but is not ideal for everyone. Larger, active individuals need more than 64 oz to stay hydrated, especially in warm climates. The 8 glasses rule may work as a baseline, but optimal intake depends on your specific needs.
Signs of dehydration
Mild dehydration occurs when you lose around 2% of your body weight in fluid. Symptoms can include:
- Thirst
- Fatigue
- Dry mouth
- Dizziness
- Headache
- Muscle cramps
- Dark yellow urine
Severe dehydration happens when fluid losses exceed 5% of body weight. Concerning signs include:
- Extreme thirst
- Weakness or lightheadedness
- Confusion
- Shriveled skin
- Infrequent urination
- Fever
- Rapid heart rate
- Rapid breathing
- Low blood pressure
- Fainting
Dehydration can progress quickly in babies, small children, older adults and people with underlying conditions. Seek medical care immediately for severe dehydration.
Tips for staying hydrated
Here are some tips to help you meet daily water needs:
- Drink a glass of water with each meal and snack.
- Carry a reusable water bottle for easy sipping throughout the day.
- Choose water or other unsweetened beverages instead of sugary drinks.
- Eat your water – foods like fruits, veggies and broths add hydration.
- Drink before, during and after exercise.
- Drink more in hot weather or at high altitudes.
- Monitor urine color – light yellow means you’re well hydrated.
- Weigh yourself before and after exercise to check for fluid losses.
Remember, if you’re thirsty then you’re already dehydrated. Staying hydrated takes conscious effort, so make drinking water a habit.
Can you drink too much water?
Most people’s kidneys can excrete up to 0.7-1.0 liters of urine per hour, so excess water is cleared quickly. But drinking too much too fast can be dangerous.
Overhydration, or hyponatremia, happens when excess water reduces sodium levels in the blood. This causes cells to swell and leads to symptoms like:
- Headache
- Nausea
- Vomiting
- Confusion
- Fatigue
- Muscle weakness or cramps
- Restlessness
- Seizures
Drinking over 1-2 gallons per day or excessive amounts during exercise can put you at risk. Certain medications, health conditions and endurance sports also raise the chances of overhydration and water intoxication.
Tips to avoid overhydration
- Drink when thirsty rather than forcing intake.
- Avoid exceeding recommended maximums.
- Include electrolytes from food and beverages.
- Monitor urine color – very light or clear urine may mean overhydration.
- Weigh before and after long exercise sessions.
Unless you have an unusually high metabolism or perspire heavily, drinking much more than 2 gallons per day isn’t necessary and may be harmful.
The bottom line
Staying properly hydrated is crucial for your health and well-being. Make a habit of drinking plenty of water and other unsweetened beverages throughout the day. Drink more in hot weather or with physical activity. Let thirst guide your intake, and aim for light yellow urine.
While recommendations vary, a reasonable goal is 64-128 oz (2-4 liters) per day. But optimal intake depends on your age, gender, activity level and other factors. Drink enough to prevent dehydration symptoms, but avoid overdoing it.
