The National Academies of Sciences, Engineering, and Medicine (NASEM) recommends an average daily water intake of about 3.7 liters (0.97 gallons, 4.93 bottles, or 15.6 cups) for adult men and approximately 2.7 liters (0.71 gallons, 3.6 bottles or 11.41 cups) for adult women. These guidelines are provided in the NASEM report titled ‘Report Sets Dietary Intake Levels for Water, Salt, and Potassium To Maintain Health and Reduce Chronic Disease Risk'.
However, there's no one-size-fits-all answer to optimal hydration. It varies depending on factors like activity level, climate, individual differences, and age. Remarkably, 60% of an adult's body weight comprises water, underlining its essential role. For instance, if you weigh 200 lbs (about 90.7 kg), around 120 lbs (about 54.4 kg) are water.
Our bodies need water for everything, from maintaining blood circulation to lubricating joints and aiding digestion. After all, staying hydrated isn't just a passing trend—it's an absolute necessity for life. Therefore, determining your own hydration requirements deserves careful attention.
What Factors Affect Daily Water Intake?
The factors that affect your daily water intake include your geographical location, diet, level of physical activity, health condition, whether you are pregnant or breastfeeding, and age.
- Geographical location: In hot countries like Qatar, where temperatures can reach up to 99°F (37°C), people sweat more than in cooler countries like the Netherlands, where temperatures rarely exceed 70°F (21°C). This means that people in hot countries need to drink more water to replace the fluid they lose through sweating.
- Diet: Foods rich in water content, such as fruits like watermelon and oranges, and vegetables like lettuce and cucumbers, contribute to hydration by providing essential nutrients and water. Diets high in fiber, found in whole grains, legumes, and fruits, require an adequate water intake to aid digestion and prevent constipation. Similarly, sodium-rich foods, such as processed foods (like canned soups and snacks), fast food, restaurant dishes, packaged sauces, and certain types of bread, can heighten thirst, especially when fluid retention is needed. Beverages with caffeine, such as coffee, tea, and energy drinks, can lead to dehydration by increasing urine output, while spicy and salty foods trigger thirst due to taste bud stimulation.
- Level of physical activity: Engaging in physical activities of varying intensities significantly impacts your fluid requirements. During moderate exercises such as brisk walking, light jogging, folding laundry, or washing dishes, your body sweats to cool down, necessitating additional water intake to replace lost fluids. Intense workouts like running, cycling, or high-intensity interval training (HIIT), result in even more substantial fluid loss through sweating, demanding even higher water consumption compared to individuals who are sedentary or not engaging in physical activity.
- Health conditions: During illness or fever, increased sweating can lead to fluid loss, requiring higher water consumption to prevent dehydration. Conditions like urinary tract infections or kidney stones often require increased water intake to help dilute urine and aid in preventing the formation of kidney stones. People with diabetes need to manage their water intake, if blood sugar levels are high, they may experience increased urination, resulting in fluid loss. On the other hand, heart-related conditions might require fluid restriction or increased intake based on medications.
- Pregnancy or breastfeeding: Pregnant women require additional water intake to support the growth and development of the fetus, maintain amniotic fluid levels, and facilitate increased blood volume, as outlined in the study entitled “Nutrition Column: An Update on Water Needs during Pregnancy and Beyond.” Moreover, breastfeeding mothers require additional hydration to replenish what is lost through the production and secretion of breast milk.
How Much Water Should Adults Drink Per Day?
For adults, the recommended daily water intake is about 3.7 liters (125 ounces or 4.93 bottles or 15.6 cups) for men and approximately 2.7 liters (91 ounces, 3.6 bottles or 11.41 cups) according to the National Academies of Sciences, Engineering, and Medicine (NASEM).
The difference in recommended daily water intake between men and women is influenced by a range of physiological and metabolic factors. Research published in the American Physiological Society Journal indicates that men generally possess a higher lean body mass of approximately 36% and a greater metabolic rate (1,740 +/- 194 kcal/day) in comparison to women (1,348 +/- 125 kcal/day). These distinctions signify that men typically require a greater amount of water for their bodily maintenance.
Moreover, according to a study entitled “Gender Differences in the Sweat Response During Spinning Exercise” by the Journal of Strength and Conditioning Research, men exhibit higher sweat rates (1.12 L.h(-1)) as opposed to women (0.57 L.h(-1)), owing to their 10-30% larger body surface area and heightened levels of physical activity on average.
How Much Water Should Older Adults Drink Per Day?
The suggested daily water intake for older adults (≥60 years) is approximately 0.88 to 1.18 liters (30-40 ounces, 1.18-1.57 bottles, or 6-8 glasses), as advised by WebMD. Despite this, the U.S. Centers for Disease Control and Prevention (CDC) does not provide a specific guideline for plain water consumption for older adults due to the insufficient scientific evidence available to support the establishment of a specific recommended fluid range.
However, when considering fluid intake for older adults, The National Council on Aging (NCOA) provides a valuable guideline. They propose a straightforward rule: aim to consume about one-third of your body weight in fluid ounces. For instance, if your weight is 200 pounds (90.7 kg), the recommendation would be to aim for around 66.6 ounces (8.3 glasses, 1.63 bottles, or 1.96 liters) of fluids each day. This approach helps older adults stay adequately hydrated.
In older adults, the sense of thirst diminishes, potentially leading to a decreased awareness of their body's fluid needs, as noted by the NCOA. This change in thirst sensation is one reason why older adults might not always feel as thirsty or remember to drink enough water compared to when they were younger.
By the time an older adult feels thirsty, that’s already an indication of early dehydration.
Anne Vanderbilt, CNS, geriatric clinical nurse specialist from Cleveland Clinic
How Much Water Should Boys Drink Per Day?
For boys aged 4 to 8 years, the recommended daily water intake is approximately 1.2 liters (5 cups or 40 ounces), as suggested by the Better Health Channel (BHC), authorized by the Department of Health, State Government of Victoria, Australia. As they grow older, boys aged 9 to 13 should aim for about 1.6 liters (around 6 cups or 48 ounces) of water each day to maintain healthy hydration.
Similarly, for boys aged 14 to 18 years, it's recommended to intake 1.9 liters (approximately 7 to 8 cups or 56 to 64 ounces) of water daily.
How Much Water Should Girls Drink Per Day?
For girls aged 4 to 8 years, the recommended daily water intake is around 1.2 liters (5 cups or 40 ounces), according to the Better Health Channel (BHC). As girls progress to the ages of 9 to 13, it's advised to aim for about 1.4 liters (approximately 5-6 cups or 40-48 ounces) of water daily to ensure proper hydration.
Likewise, girls aged 14-18 years are advised to have a daily water intake of 1.6 liters (about 6 cups or 54.1 ounces).
A study conducted by Cody Shopper, titled “Hydration markers and water intake in 3 to 13-year-old girls,” revealed that out of 39 girls aged 9 to 13 years, 60% did not consume the recommended daily amount of water (which is around 2.1 liters or 9 cups or 72 fluid ounces) as suggested by The National Academy of Medicine (NAM), also known as Institute of Medicine (IOM). Furthermore, 39% of the girls did not drink enough water. The study also found that those who drank more water showed lower concentration levels in their urine, indicating better hydration.
How Much Water Should Athletes Drink?
For athletes, the American Council on Exercise (ACE) recommends the following hydration guidelines:
- Pre-exercise: Drink 17-20 ounces (about 2.1-2.5 cups or 0.53-0.63 bottles) of water 2 hours before the start of the exercise and drink 8 ounces (around 1 cup or 0.25 bottles) 20 to 30 mins before exercise or during warm-up.
- During exercise: Drink 7 to 10 ounces (around 0.87-1.25 cups or 0.22-0.31 bottles) of water every 10 to 20 minutes.
- Post-exercise: Consume an additional 8 ounces (approximately 1 cup or 0.25 bottles) of fluid within 30 minutes.
The ACE recommends that male athletes should aim for roughly 11.7, 16oz water bottles, which is about 5.7 liters per workout day. Female athletes should aim for about 8.25 bottles of 16oz water each, totaling around 4.0 liters.
It's important to note that the hydration needs of athletes can vary depending on factors such as exercise intensity, duration, surrounding environmental conditions, and individual sweat rates. As a general guideline, athletes are often advised to follow the “sweat and replace” principle. For example, if an athlete weighs themselves before and after a workout and observes a weight reduction of 1 pound (approximately 16 ounces or 0.47 liters), they should aim to consume around 16 to 24 ounces (about 2 to 3 cups, 0.47 to 0.76 liters, or 0.5 to 0.75 bottles) of fluid to replenish the lost fluids and maintain proper hydration, as advised by ACE.
How Much Water Should Teens Drink Per Day?
According to the American Academy of Pediatrics (AAP), teenage boys aged 14 to 18 should aim for about 2.6 liters (around 11 cups or 88 ounces) of fluids per day, while teenage girls aged 14 to 18 should aim for about 1.8 liters (around 7.6 cups or 61 ounces) of fluids daily. It's important to note that these amounts include all fluids consumed, not just plain water.
Teenage boys are composed of approximately 60% water, while teenage girls have around 55% water of their body weight that's stored in the brain and heart (~73%), lungs (~83%), skin (~64%), muscles and kidneys (~79%), and bones (~31%), as reported by United States Geological Survey (USGS). This means that teenage boys have about 60 liters (15.85 gallons) of water in their bodies if they weigh 100 kilograms, while teenage girls have about 55 liters (14.52 gallons) of water in their bodies if they weigh 100 kilograms. Even a slight dehydration of 1-2% can significantly affect both physical and cognitive performance.
During adolescence, significant growth occurs, both in terms of physical development and mental capabilities. Adequate hydration is essential to support these dynamic changes. Teenagers who participate in school activities, sports, and social interactions experience increased fluid loss through processes like sweating. A study titled “The Hydration Equation: Update on Water Balance and Cognitive Performance” published by ACSM’s Health & Fitness Journal indicates that dehydration or excessive fluid loss can negatively impact both physical and cognitive functions, affecting both children and adults.
How Much Water Should You Drink Based On Your Weight?
To determine your optimal water intake based on your weight, you can follow a straightforward calculation suggested by Western Kentucky University (WKU). Start by knowing your weight in pounds (or, if you prefer, in kilograms by dividing your weight in pounds by 2.205). Then, multiply that number by 0.67 (or 67%). For example, if you weigh 200 lbs (90.7 kg), your goal should be about 134 ounces (16.8 cups, 4.0 liters, or 5.36 bottles) of water each day. If your weight is 100 lbs (45.4 kg), then you should aim for around 67 ounces (8.4 cups, 2.0 liters, or 2.68 bottles) of water daily.
Remember, it's essential to adapt this baseline by adding 12 ounces (1.5 cups, 0.35 liters, or 0.47 bottles) for every 30 minutes of exercise you do and during times when you're sweating due to hot weather.
| Weight | Recommended Water Intake |
|---|---|
| 100 lbs (45.4 kg) | 67 ounces (8.4 cups, 2.0 liters, 2.68 bottles) |
| 110 lbs (49.9 kg) | 74 ounces (9.25 cups, 2.2 liters, 2.96 bottles) |
| 120 lbs (54.4 kg) | 80 ounces (10 cups, 2.4 liters, 3.2 bottles) |
| 130 lbs (58.9 kg) | 87 ounces (10.88 cups, 2.6 liters, 3.47 bottles) |
| 140 lbs (63.5 kg) | 94 ounces (11.75 cups, 2.8 liters, 3.74 bottles) |
| 150 lbs (68.0 kg) | 100 ounces (12.5 cups, 3.0 liters, 4.0 bottles) |
| 160 lbs (72.6 kg) | 107 ounces (13.38 cups, 3.2 liters, 4.27 bottles) |
| 170 lbs (77.1 kg) | 114 ounces (14.25 cups, 3.4 liters, 4.54 bottles) |
| 180 lbs (81.6 kg) | 121 ounces (15.13 cups, 3.6 liters, 4.81 bottles) |
| 190 lbs (86.2 kg) | 127 ounces (15.88 cups, 3.8 liters, 5.08 bottles) |
| 200 lbs (90.7 kg) | 134 ounces (16.8 cups, 4.0 liters, 5.36 bottles) |
| 210 lbs (95.3 kg) | 141 ounces (17.63 cups, 4.2 liters, 5.63 bottles) |
| 220 lbs (99.8 kg) | 148 ounces (18.5 cups, 4.4 liters, 5.9 bottles) |
| 230 lbs (104.3 kg) | 154 ounces (19.25 cups, 4.6 liters, 6.17 bottles) |
| 240 lbs (108.9 kg) | 161 ounces (20.13 cups, 4.8 liters, 6.44 bottles) |
| 250 lbs (113.4 kg) | 168 ounces (21.0 cups, 5.0 liters, 6.72 bottles) |
How Much Water Should Babies Drink Per Day?
For infants up to 6 months of age, the recommended daily fluid intake is about 0.7 liters (around 3 cups, 24 ounces, or 2.36 bottles) as per the Better Health Channel (BHC). This fluid intake primarily consists of breast milk or infant formula. As they progress to the 7 to 12 months range, the suggested intake increases to around 0.8 liters (about 3.4 cups, 27.1 ounces, or 2.67 bottles) in total, with 0.6 liters (approximately 2.5 cups, 20.3 ounces, or 2 bottles) coming from fluids.
For toddlers aged 1 to 3 years, both baby girls and boys are advised to drink about 1 liter of fluids (roughly 4 cups, 32 ounces, or 3.17 bottles) per day, according to the BHC.
A study titled “Effect of varying water intake on renal function in healthy preterm babies,” which included 10 healthy premature infants (gestation 29 to 34 weeks; birthweight 1.19 to 2.19 kg), concluded that even preterm babies could effectively handle daily water intakes between 96 to 200 ml/kg (approximately 0.04 to 0.09 fluid ounces per pound of body weight), starting from the third day of life.
What Are the Signs That Help Figuring Out Your Hydration Level?
Three main signs that help determine hydration level in healthy people include the color of urine, frequency of urination (more or less than 7-8 times), and the feeling of thirst. Some additional signs to watch out for can be a dry mouth and lips, headaches, feeling tired and sluggish, dizziness, dry skin, and dark circles around your eyes.
If your urine color is pale yellow, it typically indicates that you are adequately hydrated. But, if your urine is darker yellow or amber-colored, it might signal a potential need for increased fluid intake. On the other hand, if your urine is clear or very light yellow, it could suggest that you are over-hydrated, as reported in a study titled “The Effect of Hydration on Urine Color Objectively Evaluated in CIE Lab* Color Space.”
The Cleveland Clinic suggests that most people pee about seven to eight times a day on average. If you're urinating more often or less than this, it might mean you're either drinking too much or less water.
Lastly, thirst is your body's way of telling you that you need to drink some water to quench that thirst and hydrate your body. However, it's important to note that it's not necessarily a sign of dehydration, as explained by Simone Sonnier from The University of Texas Health Science Center.
What Happens If You Don’t Drink Enough Water?
If you don't consume enough water, you can experience several health issues and symptoms, including:
- Kidney Stones: When you don't drink enough fluids, your body produces less but concentrated urine which can increase the risk of kidney stone formation, as highlighted in a study titled “The role of fluid intake in the prevention of kidney stone disease: A systematic review over the last two decades.”
- Constipation: Dehydration is one of the primary factors that cause constipation. When your body is dehydrated, the colon absorbs water from the waste material passing through. This can result in harder and drier stools, making it difficult to have regular and comfortable trips to the bathroom.
- Fatigue and Mood Changes: Not drinking enough water can lead to feelings of tiredness and potential mood changes. The British Journal of Nutrition conducted a study titled “Mild Dehydration Impairs Cognitive Performance and Mood of Men,” which showed that dehydration in men, even without hyperthermia, led to negative changes in mood, increased fatigue, and heightened anxiety.
- Headaches: Dehydration is a common trigger for headaches. Approximately 40% of people may suffer from headaches when they don't consume enough fluids, according to a 2018 study titled “Public knowledge of dehydration and fluid intake practices: variation by participants' characteristics.”
- Dark Urine: When you don't drink enough water, your urine becomes darker. However, a 2019 Greek study entitled “Fluctuation of Water Intake and of Hydration Indices during the Day in a Sample of Healthy Greek Adults.” found that there is fluctuation in urine concentration even if a person drinks the same amount of water every day, so don’t worry if your urine isn’t always clear as a mountain stream.
- Sore Throat and Bad Breath: Dehydration can lead to decreased and thick saliva production, resulting in a dry or sore throat and bad breath.
- Light-Headedness: Feeling dizzy or light-headed can also be a sign of dehydration. Proper hydration helps maintain stable blood pressure and circulation.
- Reduced Physical Performance: Dehydration can have a negative effect on physical performance, endurance, and strength, whether during exercise or everyday tasks such as walking and working. A study published in the Journal of Sport and Health Science titled “The Effects of Fluid Loss on Physical Performance: A Critical Review” found that dehydration can significantly impact activities that last longer than 30 seconds, but has less of an impact on activities that last only 15 seconds.
Is it Possible to Overhydrate Yourself?
Yes, it's possible to overhydrate yourself. However, most people aren't at risk of overhydration as long as their pituitary gland, kidneys, liver, and heart are functioning properly. According to James L. Lewis III, MD from MSD Manuals, a young adult with normal kidney function would have to regularly consume more than 6 gallons (approximately 23 liters) of water a day to go beyond the body's capacity to handle excess water.
Overhydration is more commonly seen in people with impaired kidney function, who may struggle to properly excrete excess urine, as well as those with pre-existing kidney, heart, or liver problems. Additionally, certain athletes, particularly those engaged in endurance activities such as cycling tours or ultra running, can also be susceptible to overhydration.
When overhydration happens it can lead to hyponatremia which is an abnormally low level of sodium in the blood. This occurs because the large volume of water in the body dilutes sodium to potentially dangerous levels. Symptoms of hyponatremia include confusion, headaches, fatigue, nausea, and vomiting.
