Experts recommend that males consume 15.5 cups (3.7 liters) of water daily and females 11.5 cups (2.7 liters). But environmental factors such as temperature and other health conditions may affect your water needs. Your body is about 60 percent water.
The body constantly loses water throughout the day, mainly through urine and sweat, but also from regular body functions like breathing. To prevent dehydration, you must get plenty of water from drinking and eating daily.
Experts have conflicting opinions on how much water you should drink daily. Health experts used to recommend eight 8-ounce glasses, which equals about 2 liters, or half a gallon a day. This is called the 8×8 rule and is very easy to remember.
But, some experts now believe you need to sip on water constantly throughout the day, even when you’re not thirsty. As with most things, this depends on the individual. Many factors (both internal and external) ultimately affect how much water you need. This article takes a look at some water intake studies to separate fact from fiction and explains how to easily stay well hydrated for your individual needs.
How much water do you need?
How much water you need depends on a lot of things and varies from person to person. For adults, the general recommendation from The U.S. National Academies of Sciences, Engineering, and Medicine is about:
- 11.5 cups (2.7 liters) a day for women
- 15.5 cups (3.7 liters) a day for men
- Where you live: You will need more water in hot, humid, or dry areas. You’ll also need more water if you live in the mountains or at a high altitude (4).
- Your diet: If you drink a lot of coffee and other caffeinated beverages you might lose more water through extra urination. You may also need to drink more water if your diet is high in salty, spicy, or sugary foods. Or, more water is necessary if you don’t eat a lot of hydrating foods like fresh or cooked fruits and vegetables.
- The temperature or season: You may need more water in warmer months than cooler ones due to perspiration.
- Your environment: If you spend more time outdoors in the sun or hot temperatures or in a heated room, you might feel thirstier faster.
- How active you are: If you are active during the day or walk or stand a lot, you’ll need more water than someone who’s sitting at a desk. If you exercise or do any intense activity, you will need to drink more to cover water loss.
- Your health: If you have an infection or a fever, or if you lose fluids through vomiting or diarrhea, you will need to drink more water. If you have a health condition like diabetes you will also need more water. Some medications like diuretics can also make you lose water.
- Pregnant or breastfeeding: If you’re pregnant or nursing your baby, you’ll need to drink extra water to stay hydrated. Your body is doing the work for two (or more), after all.
Does water intake affect energy levels and brain function?
Many people claim that if you don’t stay hydrated throughout the day, your energy levels and brain function start to suffer. One older study in females showed that a fluid loss of 1.36 percent after exercise impaired mood and concentration and increased the frequency of headaches (5).
A more recent study in China that followed 12 male university students found that not drinking water for 36 hours had noticeable effects on fatigue, attention and focus, reaction speed, and short-term memory (6). Even mild dehydration can reduce physical performance. Dehydration occurs when your body loses more water than you consume and can cause symptoms including fatigue and headache. A clinical study on older, healthy men reported that just a 1 percent loss of body water reduced their muscle strength, power, and endurance (7).
Losing 1 percent of body weight might not seem like a lot, but it’s a significant amount of water to lose. This usually happens when you’re sweating a lot or in a very warm room and not drinking enough water.
Does drinking a lot of water help you lose weight?
There are many claims that drinking more water may reduce body weight by increasing your metabolism and curbing your appetite.
According to research, drinking more water than usual correlated to a decrease in body weight and body composition scores. (8). Another review of studies found that chronic dehydration was associated with obesity, diabetes, cancer, and cardiovascular disease (9).
Researchers in another older study estimated that drinking 68 ounces (2 liters) in one day increased energy expenditure by about 23 calories per day due to a thermogenic response, or faster metabolism. The amount was incremental but could add up over time (10).
Drinking water about a half hour before meals can also reduce the number of calories you end up consuming. This might happen because it’s easy for the body to mistake thirst for hunger (11).
One 2010 study in middle age and older adults showed that people who drank 17 ounces (500 mL) of water before each meal lost 44% more weight over 12 weeks, compared to those who didn’t. A more recent study in young men showed that people who drank about 19 ounces (568 mL) of water before each meal reduced the amount that the participants needed to eat during the meal to feel sated (12, 13).
Overall, it seems that drinking adequate amounts of water, particularly before meals, may give you a boost in managing appetite and maintaining a moderate body weight, especially when combined with a balanced eating plan. What’s more, drinking plenty of water has a number of other health benefits.
Does more water help prevent health problems?
Drinking enough water is required for your body to function in general. Several health problems may also respond well to increased water intake:
- Constipation: Increasing water intake can help constipation (14, 15).
- Urinary tract infections: Recent studies have shown that increasing water consumption may help prevent recurring urinary tract and bladder infections (16, 17)
- Kidney stones: An older study concluded that high fluid intake decreased the risk of kidney stones, though more research is needed (18).
- Skin hydration: Studies show that more water leads to better skin hydration, though more research is needed on improved clarity and effects on acne (19)
Do other fluids count toward your total?
Plain water is not the only drink that contributes to your fluid balance. Other beverages and foods can have a significant effect. One myth is that caffeinated drinks, such as coffee or tea, don’t help you hydrate because caffeine is a diuretic.
Studies show that the diuretic effect of these beverages is weak, but they can cause extra urination in some people (20). But even caffeinated drinks help add water to your body overall.
Most foods contain water in varying levels. Meat, fish, eggs, and especially fruits and vegetables all contain water. Together, coffee or tea and water-rich foods can help maintain your fluid balance.
Indicators of hydration
Maintaining water balance is essential for your survival. For this reason, your body has a sophisticated system for controlling when and how much you drink. When your total water content goes below a certain level, thirst kicks in.
This is carefully balanced by mechanisms similar to breathing — you don’t need to think about it consciously. Your body knows how to balance its water levels and when to signal you to drink more.
While thirst may be a reliable indicator of dehydration, relying on feeling thirsty may not be adequate for optimal health or exercise performance (21). When thirst strikes, you may already feel the effects of too little hydration, such as fatigue or headaches.
There is no science behind the 8×8 rule, which has been debunked by older research. Certain circumstances may call for increased water intake (1, 24). The most important one may be during times of increased sweating. This includes exercise and hot weather, especially in a dry climate.
You can replenish the lost fluid with water if you’re sweating a lot. Athletes doing long, intense exercises may also need to replenish electrolytes, like sodium and other minerals, and water. Your water needs increase during pregnancy and while breastfeeding. You also need more water when you have a fever and when you’re vomiting or have diarrhea. If you desire to lose weight, consider upping your water intake too.
Furthermore, older people may need to consciously watch their water intake because the thirst mechanisms can start to malfunction with aging. Studies show that adults over 65 are at a higher risk for dehydration (25).
The bottom line
At the end of the day, no one can tell you exactly how much water you need. This depends on many factors.
Try experimenting to see what works best for you. Some people may function better with more water than usual, while for others it only results in more frequent trips to the bathroom.
If you want to keep things simple, these guidelines should apply to the majority of people:
- Drink often enough throughout the day for clear, pale urine.
- When you’re thirsty, drink.
- During high heat and exercise and other mentioned indications, make sure to drink enough to compensate for the lost or extra needed fluids.
- That’s it!
By Kris Gunnars