How much water should you drink a day? When the temperature outdoors soars, you’re surely aware that it’s critical to drink enough of water. Regardless of the temperature, staying hydrated is a daily requirement. Unfortunately, many of us, especially older individuals, are not getting enough to drink. “Thirst is not as strong in older folks as it was when they were younger. And if they’re using a diuretic or other drug that can promote fluid loss, this could be an issue “Dr. Julian Seifter, a kidney specialist at Harvard Medical School and an associate professor of medicine, agrees.
What the benefits of drinking water
Water keeps every system in the body functioning properly. The Harvard Medical School Special Health Report 6-Week Plan for Health Eating notes that water has many important jobs, such as:
- carrying nutrients and oxygen to your cells
- flushing bacteria from your bladder
- aiding digestion
- preventing constipation
- normalizing blood pressure
- stabilizing the heartbeat
- cushioning joints
- protecting organs and tissues
- regulating body temperature
- maintaining electrolyte (sodium) balance.
Giving your body enough fluids to carry out those tasks means that you’re staying hydrated.
If you don’t drink enough water each day, you risk becoming dehydrated. Warning signs of dehydration include weakness, low blood pressure, dizziness, confusion, or urine that’s dark in color.
So how much water should you drink? Most people need about four to six cups of water each day.
- It lubricates the joints
Cartilage, found in joints and the disks of the spine, contains around 80 percent water. Long-term dehydration can reduce the joints’ shock-absorbing ability, leading to joint pain.
- It forms saliva and mucus
Saliva helps us digest our food and keeps the mouth, nose, and eyes moist. This prevents friction and damage. Drinking water also keeps the mouth clean. Consumed instead of sweetened beverages, it can also reduce tooth decay.
- It delivers oxygen throughout the body
Blood is more than 90 percent water, and blood carries oxygen to different parts of the body.
- It boosts skin health and beauty
With dehydration, the skin can become more vulnerable to skin disorders and premature wrinkling.
- It cushions the brain, spinal cord, and other sensitive tissues
Dehydration can affect brain structure and function. It is also involved in the production of hormones and neurotransmitters. Prolonged dehydration can lead to problems with thinking and reasoning.
- It regulates body temperature
Water that is stored in the middle layers of the skin comes to the skin’s surface as sweat when the body heats up. As it evaporates, it cools the body. In sport.
Some scientists have suggested that Trusted Source when there is too little water in the body, heat storage increases and the individual is less able to tolerate heat strain.
Having a lot of water in the body may reduce physical strain if heat stress occurs during exercise. However, more research is needed into these effects.
- The digestive system depends on it
The bowel needs water to work properly. Dehydration can lead to digestive problems, constipation, and an overly acidic stomach. This increases the risk of heartburn and stomach ulcers.
- It flushes body waste
Water is needed in the processes of sweating and removal of urine and feces.
- It helps maintain blood pressure
A lack of water can cause blood to become thicker, increasing blood pressure.
- The airways need it
When dehydrated, airways are restricted by the body in an effort to minimize water loss. This can make asthma and allergies worse.
- It makes minerals and nutrients accessible
These dissolve in water, which makes it possible for them to reach different parts of the body.
- It prevents kidney damage
The kidneys regulate fluid in the body. Insufficient water can lead to kidney stones and other problems.
- It boosts performance during exercise
How much water should you drink a day?
The daily four-to-six cup rule is for generally healthy people. It’s possible to take in too much water if you have certain health conditions, such as thyroid disease or kidney, liver, or heart problems; or if you’re taking medications that make you retain water, such as non-steroidal anti-inflammatory drugs (NSAIDs), opiate pain medications, and some antidepressants.
How much water a day should you drink if you fit into that category? There’s no one-size-fits-all answer. Dr. Seifter says water intake must be individualized, and you should check with your doctor if you are not sure about the right amount for you.
But even a healthy person’s water needs will vary, especially if you’re losing water through sweat because you’re exercising, or because you’re outside on a hot day. If you’re wondering how much water you should drink on those occasions, speak with your doctor, but a general rule of thumb for healthy people is to drink two to three cups of water per hour, or more if you’re sweating heavily.
Tips for avoiding dehydration
It’s not just water that keeps you hydrated. All beverages containing water contribute toward your daily needs. And it’s a myth that caffeinated beverages or those containing alcohol are dehydrating because they make you urinate. They do, but over the course of the day, the water from these beverages still leads to a net positive contribution to total fluid consumption.
Of course, there are many reasons why water is still the better choice. Remember, sugary drinks can lead to weight gain and inflammation, which can increase your risk for developing diseases such as diabetes. Too much caffeine can give you the jitters or keep you from sleeping. And, alcohol intake should be limited to one drink per day for women, and 1-2 drinks per day for men.
To ward off dehydration, drink fluids gradually, throughout the day. An easy way to do this is to have a drink at each meal, as well as socially, or with medicine.
And know that you also get fluids from water-rich foods, such as salads, fruit, and applesauce.
Whether you’ve had fatigue or even dry skin, you’ve probably been told to drink more water as a cure. But this advice comes from decades-old guidance… and may have no scientific basis.
As many countries urge populations to stay at home, many of us are paying more attention to our diets and how the food we eat can support our health. To help sort out the fact from the fiction, BBC Future is updating some of our most popular nutrition stories from our archive.
Our colleagues at BBC Good Food are focusing on practical solutions for ingredient swaps, nutritious storecupboard recipes and all aspects of cooking and eating during lockdown.
In the early 19th Century, people had to be close to death before deigning to drink water. Only those “reduced to the last stage of poverty satisfy their thirst with water”, according to Vincent Priessnitz, the founder of hydropathy, otherwise known as “the water cure”.
Many people, he added, had never drunk more than half a pint of plain water in one sitting.
How times have changed. Adults in the UK today are consuming more water now than in recent years, while in the US, sales of bottled water recently surpassed sales of soda. We’ve been bombarded with messages telling us that drinking litres of water every day is the secret to good health, more energy and great skin, and that it will make us lose weight and avoid cancer.
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Commuters are encouraged to take bottles of water onto the London Underground, school pupils are advised to bring water into their lessons and few office meetings can commence without a giant jug of water sitting in the middle of the desk.
Fuelling this appetite for water is the “8×8 rule”: the unofficial advice recommending we drink eight 240ml glasses of water per day, totalling just under two litres, on top of any other drinks.
That “rule”, however, isn’t backed by scientific findings – nor do UK or EU official guidelines say we should be drinking this much. To add to the confusion, as the current pandemic took hold people were advised to tap a sip of warm water every 15 minutes to protect against the virus – advice that has no basis in fact.
Why is there so much unclear information about how much water to drink? Most likely, it seems, from misinterpretations of two pieces of guidance – both from decades ago.
In 1945 the US Food and Nutrition Board of the National Research Council advised adults to consume one millilitre of liquid for every recommended calorie of food, which equates to two litres for women on a 2,000-calorie diet and two-and-a-half for men eating 2,500 calories. Not just water, that included most types of drinks – as well as fruits and vegetables, which can contain up to 98% water.
In 1974, meanwhile, the book Nutrition for Good Health, co-authored by nutritionists Margaret McWilliams and Frederick Stare, recommended that the average adult consumes between six to eight glasses of water a day. But, the authors wrote, this can include fruit and veg, caffeinated and soft drinks, even beer.
In thirst we trust
Water is, of course, important. Making up around two-thirds of our body weight, water carries nutrients and waste products around our bodies, regulates our temperature, acts as a lubricant and shock absorber in our joints and plays a role in most chemical reactions happening inside us.
We’re constantly losing water through sweat, urination and breathing. Ensuring we have enough water is a fine balance, and crucial to avoiding dehydration. The symptoms of dehydration can become detectable when we lose between 1-2% of our body’s water and we continue to deteriorate until we top our fluids back up. In rare cases, such dehydration can be fatal.
Experts largely agree that we don’t need any more fluid than the amount our bodies signal for, when it signals for it
Years of unsubstantiated claims around the 8×8 rule have led us to believe that feeling thirsty means we’re already dangerously dehydrated. But experts largely agree that we don’t need any more fluid than the amount our bodies signal for, when it signals for it.
“The control of hydration is some of most sophisticated things we’ve developed in evolution, ever since ancestors crawled out of sea onto land. We have a huge number of sophisticated techniques we use to maintain adequate hydration,” says Irwin Rosenburg, senior scientist at the Neuroscience and Ageing Laboratory at Tufts University in Massachusetts.
In a healthy body, the brain detects when the body is becoming dehydrated and initiates thirst to stimulate drinking. It also releases a hormone which signals to the kidneys to conserve water by concentrating the urine.
“If you listen to your body, it’ll tell you when it’s thirsty,” says Courtney Kipps, consultant sports physician and principal clinical teaching fellow of Sports Medicine, Exercise and Health and UCL, and medical director of Blenheim and London Triathlons.
“The myth that it’s too late when you’re thirsty is based on the supposition that thirst is an imperfect marker of a fluid deficit, but why should everything else in the body be perfect and thirst be imperfect? It’s worked very well for thousands of years of human evolution.”
While water is the healthiest option since it has no calories, other drinks also hydrate us, including tea and coffee. Although caffeine has a mild diuretic effect, research indicates that tea and coffee still contribute to hydration – and so do some alcoholic drinks. (Find out if you can eat your way out of a hangover.)
Drinking to good health
There’s little evidence suggesting that drinking more water than our body signals for offers any benefits beyond the point of avoiding dehydration.
Still, research suggests there are some important benefits to avoiding even the early stages of mild dehydration. A number of studies have found, for example, that drinking enough to avoid mild dehydration helps support brain function and our ability to do simple tasks, such as problem-solving.
Some studies suggest fluid consumption can help manage weight. Brenda Davy, a professor of human nutrition, food and exercise at Virginia Polytechnic Institute and State University, has carried out a few studies looking at fluid consumption and weight.
In one study, she randomly assigned subjects to one of two groups. Both groups were asked to follow a healthy diet for three months, but only one was told to drink a 500ml glass of water half an hour before eating each meal. The group who drank the water lost more weight than the other group.
Both groups were also told to aim for 10,000 steps a day, and those who drank the glasses of water better adhered to this. Davy guesses this is because mild dehydration of around 1-2% is quite common, and many people may not realise when this happens – and even this mild level can affect our mood and energy levels.
But Barbara Rolls, a professor of intensive care medicine at University College London, says that any weight loss associated with drinking water is more likely to come from water being used as a substitute for sugary drinks.
“The notion that filling up on water before a meal will melt the pounds away is not well established, and water consumed on its own empties out of the stomach really quickly. But if you consume more water through the food you eat, such as soup, this can help fill you up as the water is bound to the food and stays in the stomach for longer,” she says.
Another alleged health benefit of drinking more water is improved skin complexion and better moisturised skin. But there is a lack of evidence to suggest a credible scientific mechanism behind this. (Read more about whether drinking extra water is good for your skin).
Too much of a good thing?
Those of us aiming for eight glasses of water per day aren’t doing ourselves any harm. But the belief we need to drink more water than our bodies signal for can sometimes become dangerous.
Too much fluid consumption can become serious when it causes a dilution of sodium in blood. This creates a swelling of the brain and lungs, as fluid shifts to try to balance out blood sodium levels. (Learn more about what happens if you drink too much water.)
Over the last decade, at least 15 athletes have died from over-hydration during sporting events
Over the last decade or so, Kipps has been aware of at least 15 cases of athletes who’ve died from over-hydration during sporting events. She suspects these cases are partly because we’ve become distrustful of our own thirst mechanism and that we think we need to drink more than our bodies are calling for to avoid dehydration.
“Nurses and doctors in hospitals will see severely dehydrated patients who have serious medical conditions or who haven’t been able to drink for days, but these cases are very different from the dehydration that people worry about during marathons,” she says.
Johanna Pakenham ran the 2018 London Marathon, the hottest on record. But she can’t remember most of it because she drank so much water during the race that she developed over-hydration, known as hyponatremia. She was rushed to hospital later that day.
“My friend and partner thought I was dehydrated and they gave me a big glass of water. I had a massive fit and my heart stopped. I was airlifted to hospital and unconscious from the Sunday evening until the following Tuesday,” she says.
Pakenham, who plans to run the marathon again this year, says the only health advice offered by friends and marathon posters was to drink lots of water.
I really want people to know that something so simple can be so deadly – Johanna Pakenham
“All it would’ve taken for me to be okay was having a few electrolyte tablets, which increase the sodium levels in your blood. I’ve ran a few marathons before and I didn’t know that,” she says.
“I really want people to know that something so simple can be so deadly.”
The idea that we must be constantly hydrated means many people carry water with them wherever they go, and drink more than their bodies require.
“The maximum a person in the hottest possible heat in the middle of the desert might sweat is two litres in an hour, but that’s really hard,” says Hugh Montgomery, director of research at the Institute for Sport, Exercise and Health in London.
Carrying around 500ml of water for a 20-minute journey on the London Underground, you’re never going to get hot enough to sweat at that rate – Hugh Montgomery
“The idea of carrying around 500ml of water for a 20-minute journey on the London Underground – you’re never going to get hot enough to sweat at that rate, even if you’re dripping with sweat.”
For those who feel more comfortable going off official guidelines rather than thirst, the UK’s NHS advises drinking between six to eight glasses of fluid a day, including lower fat milk and sugar-free drinks, including tea and coffee.
First, water helps us to feel full and satiated. When we are hydrated, we tend to eat less since we don’t confuse signs of dehydration with signs of hunger. Many people actually report feeling hungry when they are in fact dehydrated.
Another added benefit of drinking water is that it is less likely that someone will overeat. When your stomach is filled with liquid from drinking water, it is less likely you will eat too much or mindlessly snack throughout the day.
Lastly, if you are focused on drinking more water, you are less likely to reach for sugary drinks and beverages with empty calories. Swapping in water for higher calorie beverages is a great way to lose weight.
More Questions and Answers About How Much Water to Drink
What liquids count towards your daily water goal?
Pretty much all liquids count towards your daily water intake goals. This includes sparkling water, juice, milk, tea, coffee, smoothies, and even soda and diet soda. However, the best and most affordable option is always plain water. And it better for your body than other beverages according to this Harvard study.
A few notes about caffeine. For a long time, people believed that drinking caffeinated beverages like coffee and tea, actually counted against your daily water intake since they are diuretics. However, recent studies suggest that this might not actually be the case.
One other important note, food also contributes to your daily water goals. Some foods, like watermelon, is almost 100% water and therefore counts as well. Since this can be hard to track, just think of food as extra water you are having every day instead of trying to track it.
How much water is too much?
Many people wonder if there is actually a point where you can drink too much water. There are some rare cases of someone over-hydrating, known as hyponatremia. However, it is very rare and usually only seen in endurance athletes who are over-drinking while doing very intense exercise or in older adults with certain health conditions.
For the average person, this is normally not a concern.
Is drinking a gallon of water bad for you?
Water poisoning or water intoxication is a condition where someone drinks too much water in a short period of time and their cells become imbalanced due to a loss of sodium. It is a serious condition but extremely rare.
General guidelines suggest that you shouldn’t drink more than 27-33 ounces of water per hour. This means drinking a gallon of water in an hour wouldn’t be recommended.
Any type of water challenge could potentially be dangerous and it is always best to listen to your body.
How much water do you really need?
At the most basic level, you should be drinking enough water every day that you do not show any symptoms of dehydration and that your body is functioning well. There is no exact number for everyone since it varies based on your body, activity level, diet, climate, and more.
Generally speaking, doctors recommend that you get at least 6 cups of water daily at a minimum but most people should be drinking more than that. One easy indicator is urine. Your urine should be fairly frequent and like yellow or clear in color. Darker or smelly urine is an indicator of dehydration and usually indicated you should be drinking more water.
Does water affect your energy levels?
Water can have a huge impact on energy levels. People who are dehydrated report feeling more tired, sluggish, and lethargic. Staying hydrated helps keep your cells functioning properly and helps energy levels stay high. In fact, it is one of the most recommended tips for boosting energy levels quickly.
Does water intake affect brain function?
Water and proper hydration have been shown to greatly benefit brain function. Specifically, staying hydrated can boost mood and mood stability, improve concentration, improve cognition, aid memory, prevent headaches, and even reduce stress.
How can I tell if you are dehydrated?
Here are some of the most common symptoms of dehydration:
- Feeling thirsty
- Dry mouth
- Change in mood
- Feeling tired or weak
- Trouble concentrating or focusing
- Increase in body temperature
- Rapid breathing and/or heartbeat
- Flushed or red skin
- Dry mouth, eyes, or lips
- Dark yellow or smelly urine (note, this isn’t solely caused by dehydration and is common after taking multivitamins or eating certain foods as well. This evens out throughout the day, so most of your urine should mostly be light or clear.)
Should I drink 8 glasses of water daily? What about the “8 by 8” rule?
To help people have a tangible amount of water to focus on, there was a push to recommend that the average person drink 8 glasses of water by 8 PM daily. This would mean that you drank at least 64 ounces of water daily.
There is no solid evidence suggesting that this is, in fact, the right amount, but it is probably a good recommendation for a minimum amount. Depending on your lifestyle, body type, diet, age, and more – this will vary.
What factors affect how much water you need daily?
The amount of water someone needs daily depends on a number of different factors. Here are the most common factors that affect water needs.
- Activity Level and exercise: People who exercise or do rigorous activity will need to consume more water daily. However, the exact amount varies depending on the activity, muscle mass, and climate.
- Climate and temperature: If you live in a hot and humid climate, or it’s a hot day, you will need more water. As we sweat and perspire, we need to replace the water we are losing.
- Diet: Diets that are higher in sodium may require more water to flush out that sodium.
- Pregnancy and breastfeeding: Pregnant and nursing moms will need more water than the average person.
How do you know if you are well hydrated?
The easiest way to know that you are well hydrated is to pay attention to your urine. Generally speaking, it should be light yellow or clear without too much of a smell. Thirst is another indicator, but many people confuse this with hunger.
What about caffeine? How does it affect water intake and hydration?
There used to be a common belief that caffeine counted against hydration since it is a diuretic. However, recent studies have shown it may not affect hydration as much as was previously thought. With that said, water is always the best option when trying to stay hydrated.
How much water do you need during exercise?
It is recommended that you drink water before, during, and after exercise. For most exercise, plain water will do. Some people recommend drinking an electrolyte drink after doing any vigorous exercise for an hour or more to replace lost electrolytes.
One other note, drinking too much water too fast during exercise can cause cramps and stomach pain. It is best to sip slowly while working out in most cases.