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How much water do you really need to drink?

We are bombarded with messages about drinking more fluids – but is it really essential? Siân Phillips, Editor of Be Healthy magazine, investigates.

The water content of our body equates to between 50% and 65%.The NHS recommend we should drink six to eight glasses of water a day to keep our bodies topped up and hydrated, but sadly most of us don’t drink enough, and we are leaving ourselves dehydrated, out of energy and prone to gaining weight.

How much water do you need to drink a day?

The NHS Eatwell guide recommends that our water intake should be around six to eight glasses of water a day. As well as water, low fat milk, sugar-free drinks - including tea and coffee - all count towards this amount. If you are using tea and coffee within your daily allowance, consider using decaffeinated drinks, as it's a healthier option. 

Why do we need to drink water?

“Your body is nearly two thirds water and so it is really important that you consume enough fluid to stay hydrated and healthy,” says the British Nutrition Foundation. “If you don’t get enough fluid you may feel tired, get headaches and not perform at your best.” A study into how well children performed in a visual attention test showed that those who did not drink water beforehand achieved a lower score than those who did.

Water is more than just a quick drink to quench your thirst, it has many amazing health benefits that most of us are missing out on.

It will boost your metabolism

Research published in the Journal of Endocrinology and Metabolism found that drinking water can boost your resting energy exposure, with some research finding increases of as much as 30% just 10 minutes after drinking. While the reasons for this boost are not fully understood, some researchers believe it could be due to the extra energy used in warming the water up to body temperature as it passes through your digestive system.

Hydration can suppress your appetite and improve weight loss

Drinking water before a meal can reduce the amount of calories consumed by as much as 13% (Source: Journal of the American Dietetic Association). This means that you will be left feeling fuller without the extra calories, making it easier to shed those pounds and helping with weight loss.

It will help you focus

Your brain is made up of around 85% of water, so having a good level of water intake will help with focus, concentration and decision-making - great for finally finishing off that tricky Sudoku!

Researchers from the University of East London found that people who were thirsty were distracted by their brain’s constant messages urging them to find water. Eased of this burden, the brain was freed up to concentrate on the task at hand.

It won’t rot your teeth

No sugar means no tooth decay. Unlike sugary soft drinks (and even fruit juice), drinking water won’t lead to a build-up of plaque on your teeth that could lead to tooth decay and even gum disease.

It’s good for your skin

Since your body is made up of mostly water, keeping yourself hydrated will leave your skin feeling hydrated and looking younger (Source: Skin Research and Technology Journal). While drinking more water won’t prevent wrinkles from developing, the increased water intake of a fully hydrated person means the skin will be firmer and more elastic, improving the appearance of wrinkles and reducing some of the visible effects of ageing.

Do I really have to drink 8 glasses of water a day?

Yes, there has been some evidence to the contrary. An article in the British Medical Journal questioned the benefits of drinking eight glasses of water a day.

It said that the recommendation may have originated from a 1945 report, which stated: “A suitable allowance of water for adults is 2.5 litres daily in most instances. An ordinary standard for diverse persons is 1 millilitre for each calorie of food.”

However, in reporting this figure it seems that the crucial next sentence – which said that most of our daily water intake could actually be obtained from food – was omitted.


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Who should I believe?

For most people, the simplest way to check whether you’re drinking enough water is to check your wee. “The best advice is to keep the urine pale yellow and be guided by thirst,” says Benenden Hospital’s consultant urologist Steve Garnett. He adds: “There is no set amount to drink as it will vary according to a person's size and activity. A small 90-year-old woman doesn't need to drink as much a large rugby player running around in hot weather.”

Conversely, signs of dehydration include dizziness or light-headedness, headaches or tiredness, and a dry mouth, lips and eyes. Additionally, if you only pass a little urine and infrequently (less often than three or four times a day) then your fluid intake may not be enough or have an underlying health issue that needs to be explored.

Is there anyone who should take special measures to drink more?

Some people need to make a concerted effort to ensure they’re drinking enough, such as the elderly, who may not have noticed that they’re becoming dehydrated. Babies and infants can quickly become dehydrated during illness or in intense heat due to their low body weight.

How much water should you drink when pregnant?

Pregnant or breastfeeding women need to ensure they’re drinking at sufficient levels, as do people who’ve had an illness resulting in vomiting or diarrhoea, or with other conditions such as a bladder infection. If the weather is particularly hot or you’ve been sweating a lot after exercise or manual work then your water and liquid requirement will increase too.

How much water should you drink a day to lose weight?

Many soft and instant drinks like hot chocolate or milkshakes, contain high levels of sugar - which means more calories. Replacing these drinks with water will reduce your daily calorie intake, which makes it easier for you to maintain or even lose weight. If you don't like the taste of water, try sparkling water with added lemon or lime. 

Is drinking too much water bad for you?

Yes. Drinking too much water can lead to a condition called hyponatraemia (also known as water intoxications), which can be fatal. Those who drink too much can develop the condition when their blood sodium levels fall too low. This can happen, for example, when athletes drink very large quantities of water after endurance sport, without replacing the sodium lost through perspiration.

For more information, check the NHS guidelines


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Medically reviewed by Cheryl Lythgoe on December 2021. Next review date: December 2022.