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Medically reviewed by Adrienne Seitz, MS, RD, LDN, Nutrition — Written by Markus MacGill — Updated on November 17, 2021 People often hear that they should drink eight glasses of water per day. However, that may not be entirely true, and the amount of water a person should drink can vary depending on their age, activity level, and more. Water is an essential part of life, but how much should a person really be drinking? The commonly touted wisdom of eight glasses of water per day may be suitable for some people, but it is not a “one-size-fits-all” recommendation. Some experts say there is a lack of scientific evidence supporting these claims. Others note that promoters include bottled water manufacturers. So, how much water does a person really need? Read more to learn how much water to drink, where to get it, and the risks of drinking too little or too much. Share on PinterestRidofranz/Getty Images Back in 1945, the U.S. Food and Nutrition Board advised people to consume 2.5 liters, or 84.5 fluid ounces (fl oz), of water per day, including fluid from prepared foods. Today, the Centers for Disease Control and Prevention (CDC) say there is no recommendation for how much plain water adults should consume daily. The 2015–2020 U.S. Dietary Guidelines do not recommend a specific daily water or fluid intake, but they do recommend choosing plain rather than flavored water and juices. In the United Kingdom, the National Health Service (NHS) recommends consuming 6–8 glasses of water a day, or 1.9 liters (almost 65 fl oz), including water that is in food. The NHS notes this amount is suitable for a temperate climate. It says more will be needed in hotter climates. There is no fixed amount of fluid recommended by age, but some patterns emerge among healthy individuals doing a moderate amount of activity in a temperate climate. The following sections show the average water intake for people of different ages. InfantsExperts do not recommend plain water for infants before the age of 6 months. The CDC says that if infants over 6 months of age need additional fluid on hot days, they can consume water in a bottle. However, their primary form of fluid and calories should be breast milk or formula. Children over 12 months of ageChildren over 12 months of age should be encouraged to drink water in the following situations:
Children should limit their juice consumption to one glass per day. Parents are advised to keep a pitcher handy to encourage healthy water-drinking habits, and schools should have water fountains or equivalent facilities. Adults ages 19–30 yearsThe recommended adequate intakes of total water from all sources each day for most adults between 19 and 30 years of age are:
People who are pregnant are likely to need an extra 0.3 liters (10 fl oz). Those who are breastfeeding will need an additional 0.7 to 1.1 liters (23–37 fl oz). Older adultsOlder adults may be at risk of dehydration due to health conditions, medications, loss of muscle mass, reduction in kidney function, and other factors. Older adults who are well hydrated have been found to have:
Dehydration has been linked to a higher frequency of:
People can consume water by:
Some surveys suggest that around 20 percent of water intake comes from food, and the rest is from fluids. This depends on diet. A higher intake of fresh fruit and vegetables will mean a higher intake of water from foods. Here are some examples of the water content of different foods and fluids: During exercise, people may need to consume more water than usual. The amount they should drink depends on:
Older guidance from the American College of Sports Medicine (ACSM) advises drinking water during activity to prevent dehydration that leads to a decline in body weight of more than 2 percent and changes in electrolyte balance. These changes, researchers say, can lead to reduced performance. However, a study published in the International Journal of Exercise Science concludes that a loss of up to 4 percent of water has no effect on real-world sports performance. This means that, while it is important to be hydrated before a workout — and a person should aim to replace fluid lost after exercise — drinking water during a workout may not be essential. However, if people exercise for long periods, they may benefit from consuming water or an electrolyte beverage. When should a person drink water?Most of the time, the body’s sensitive natural mechanisms maintain appropriate fluid levels. There are two main ways the body does this: (1) through thirst, which tells a person to drink more water; and (2) through urine output, in which the kidneys regulate the water we consume by either emptying it into the urinary bladder or holding onto it in the blood plasma. The kidneys also regulate the balance of electrolytes, such as sodium and potassium, in the body fluids. Additionally, they receive hormonal signals to conserve or release water into the urine if the brain detects changes in the concentration of the solutes in the blood. It is often said that people need to drink at least eight 8-ounce (oz) glasses of water per day. However, this is an overly simplistic answer to a complicated question. The body is good at regulating itself, and water is no exception. The body is constantly working to maintain a balance of water coming in and water going out. If a person drinks too much water, the body will excrete more. If they drink too little, it will excrete less. In addition to body size and activity level, other everyday factors can play a role in determining how much water a person should drink. For example, consuming more sodium and protein means a person may need to drink more water. Conversely, eating a lot of fruits and vegetables means they may not need to drink as much. Most of the time, the body will give a person cues that tell them to drink more or less fluid. The body even has a water-regulating hormone — arginine vasopressin — that manages thirst, fluid excretion, and the body’s water balance. Some people have raised concerns that consuming too much water could be dangerous. If a person drinks too much water, it could lead to hyponatremia, or water intoxication, which is when sodium levels in the blood plasma become too low. Symptoms include: Hyponatremia is rare. When it does occur, it usually affects endurance athletes, people with diabetes, and those taking certain medications. The amount of water a person needs varies based on their age, size, activities, and the temperature. Although many people follow the eight-by-eight rule, it may be outdated and overly simplistic. The body is incredibly good at maintaining its water balance, and it urges people to drink more by making them thirsty. People who work outdoors in hot climates or exercise vigorously may need to consume more water. They can also get fluid from foods high in water, such as fruits and vegetables. Last medically reviewed on November 14, 2021 Medical News Today has strict sourcing guidelines and draws only from peer-reviewed studies, academic research institutions, and medical journals and associations. We avoid using tertiary references. We link primary sources — including studies, scientific references, and statistics — within each article and also list them in the resources section at the bottom of our articles. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.
Drinking plenty of water every day is essential for good health. Australian tap water is the best choice for staying well hydrated. Why is water important for good health?Water is an essential part of a healthy balanced diet because the body relies on it to function properly. Between 50% and 80% of the human body is made up of water. All the body’s chemical processes take place in water. We need water for digestion, to absorb nutrients, to help us move, get rid of waste products and to regulate our body temperature. If the body doesn’t have enough water (known as dehydration), it won’t function as well. People who don’t drink enough water every day are at greater risk of kidney stones, problems with their heart valves and some kinds of cancer. Even minor dehydration can affect physical and mental performance. Drinking water is also essential for the health of your mouth. Drinking water in most parts of Australia contains fluoride, which helps to protect against tooth decay. Water is also needed for the body to make saliva, which is important for washing food away from the teeth and helping you chew, taste, swallow and digest food. Many functions in the human body rely on water to work properly.View the full version of this water infographic here. How much water should I drink?The amount of water that someone should drink varies greatly from person to person. It depends on how your individual metabolism works, what the temperature is, what you eat, your age and whether you have a medical condition. It’s especially important for children and older people to drink enough water. We get about one fifth of the water we need from food and the rest from drinking fluids. The body gets rid of water throughout the day through breathing and sweating, as well as by going to the toilet. As a general rule, men need about 10 cups of fluids every day and women need about 8 cups (add another cup a day if you are pregnant or breastfeeding). Babies need 0.7 to 0.8 litres of fluid a day from breast milk or formula, while children need between 4 cups (for 1-year-olds) and 6 to 8 cups a day (for teenagers). In Australia, 1 cup is equivalent to 250ml. You can get water from any fluids — including tea and coffee, fruit juice and soft drinks. But be careful how much of these you drink since they can make you put on weight, damage your teeth and have an unwanted stimulant effect. Australian tap water is always the best choice. Is bottled water healthier than tap water?Bottled water has no more health benefits than tap water. Tap water is just as safe to drink, unless there has been an incident in the area that affects the quality of the water, such as a flood or the discovery of bacteria in the supply. The fluoride in tap water is also important for healthy teeth. Many people believe bottled water is healthier because it contains added minerals. However, studies have shown that bottled water can have less magnesium, potassium and calcium than tap water. Some varieties can also contain higher levels of potentially harmful substances, including chlorine, nitrate and chemicals released from the plastic such as bisphenol A (BPA). Bottled water has lower quality controls than tap drinking water, while plastic bottles are not good for the environment. How can I stay hydrated?
To stay hydrated, it’s important to drink before you feel thirsty. This is especially important if you are exercising or if it’s a hot day. Even if you’re not thirsty, try to drink water regularly throughout the day. You can tell if you are well hydrated by the colour of your urine. If it is pale yellow or straw-coloured, you are probably hydrated. If it’s darker, you need to drink more water. You can see the colour your urine should be on this urine colour chart — but remember that taking some medicines or vitamin supplements can change the colour of your urine for a few hours. You can stay hydrated by:
Use this urine colour chart to assess how hydrated you are. What happens when you don’t drink enough water?Not drinking enough water can make you very ill. Severe dehydration can lead to dizziness and collapse. If you are showing any signs of dehydration, drink some water straight away and seek medical advice if you still don't feel better. Older people are at greater risk of dehydration because they naturally feel less thirsty and their kidneys may not work as well. Memory problems, taking some medicines such as diuretics and laxatives and not being able to move around to fetch a drink all make it harder to stay hydrated. For older people, not drinking enough water in the long term can lead to serious problems such as constipation, a decline in memory, not being able to function as well, having a fall, and having a stroke. These are the signs that you need to drink more water: Is it possible to drink too much water?In some people, drinking too much water can lead to a dangerous condition called hyponatremia, where the levels of sodium in the blood become too diluted. This can occasionally happen to people who drink too much while they’re doing intense physical activity, such as running a marathon. Babies can also have too much water if their formula is too diluted. People with chronic kidney disease, heart failure or liver disease, who cannot get rid of water from the body as efficiently, should talk to their doctor about how much water to drink. If you have some other long-term medical condition, it is also a good idea to discuss your water consumption habits with the doctor. |