How much water should I drink a day?

What are the benefits of drinking water, how much should you drink per day, and what are the symptoms of dehydration? Discover the facts in our expert guide.

A glass of water on a table

When it comes to the optimum amount of water to drink each day, everyone seems to have a different opinion. So should we be drinking 6-8 glasses, two litres, or even more? Do other liquids besides water count? And what are the warning signs that you're drinking too little water? We asked nutritionist (MBANT) Kerry Torrens for her expert opinion.

What are the benefits of drinking water?

When you stop to think that more than two thirds of your body is water, it's obvious how important it is to stay well hydrated. Hydration is needed for digestion, for our heart and circulation, for temperature control and for our brain to work well. Water is, without doubt, the single most essential component of the human body.

Drinking water may boost mental performance

Research suggests that losing as little as 1% of your body weight in fluid may reduce mental performance, as well as potentially inducing fatigue and headache. This mild level of dehydration can easily occur over the course of a normal day’s activities, which highlights how important drinking little and often is for your health.

Drinking water may boost mood

Being dehydrated can also affect our mood and mental well-being, with studies suggesting that energy levels, cognition and emotions may all be affected.

Drinking water may boost physical performance

If you exercise, some studies suggest that as little as a 2% loss in your body’s water content may impact how well you perform physically. Dehydration may compromise your body’s ability to control its temperature, increase feelings of tiredness and unsurprisingly, make exercise more difficult. However, research in this area is conflicting. One small study which kept athletes in the dark about their hydration status showed that dehydration made no difference to their performance. Clearly other factors besides temperature, climate and endurance also play an important role.

What are the symptoms of dehydration?

Thirst and passing dark-coloured urine are key signs that you may be dehydrated, as well as feeling lethargic, dizzy or having a dry mouth and lips. If you’ve been ill with diarrhoea and vomiting or fever, you can become dehydrated very quickly unless you replace the extra water lost from the body. In certain circumstances rehydration solutions can be useful because they help to replace the water, salts and minerals that your body has lost. If you are experiencing this, the NHS recommends that you consult a pharmacist who may recommend oral hydration sachets, and speak to your GP if your symptoms don't improve with treatment.

Checking the colour of your urine is widely considered to be the easiest and most practical way to assess your hydration needs – aim to pass urine which is light yellow to clear in colour.

Babies, children and the elderly are the most at risk of dehydration. Visit the NHS website to find out the signs of serious dehydration in adults and children under five years old.

Four glasses of sparkling water on a tray

How much water should you drink a day?

Each individual's needs are unique to them and depend on their health, age, size and weight as well as activity levels, the type of job they do and the climate they live in. Drinking little and often is the best way to stay hydrated. In the UK, the Eatwell Guide suggests you should aim for 6-8 glasses of water and other liquids each day to replace normal water loss – around 1.2 to 1.5 litres. Water, lower fat milk and sugar-free drinks, including tea and coffee, all count.

In March 2010, the European Food Safety Authority (EFSA) issued a report suggesting an adequate total daily intake of 2 litres of fluids for women and 2.5 litres for men. This quantity includes drinking water, drinks of all kinds and the moisture available from the food we eat. On average our food is thought to contribute about 20% of our fluid intake which, therefore, suggests a woman should aim to drink about 1.6 litres and a man should aim for 2 litres.

However, there is controversy surrounding our hydration needs. Some argue that there’s a lack of scientific evidence to support the perceived health benefits of drinking the often-touted 2 litres a day, especially when it comes to those of us who live in temperate climates and who lead a largely sedentary lifestyle. However, the NHS still recommends that we consume around 6-8 glasses, with more required in hot weather or if exercising.

Do liquids other than water count?

Water, milk, sugar-free drinks and tea and coffee all count, but remember that caffeinated drinks like tea and coffee can make the body produce urine more quickly. Fruit juice and smoothies also count, but because they contain ‘free’ sugars (the type we are encouraged to cut back on), you should limit these to a combined total of 150ml per day.

Many of the foods we eat contribute to our fluid intake – for example, dishes like soup, ice cream and jelly, as well as fruit and veg with a high water content, such as melon, courgette or cucumber.

Two cups of green tea with a tea pot

Can you drink too much water?

It is possible to go the other way and drink too much, although for most people with healthy kidneys this will be managed by urinating more frequently. Hyponatraemia is a condition caused by too much water which causes sodium levels to fall dangerously low. Athletes who participate in endurance events and take on too much fluid may be at risk of this condition.

Read more about how to stay hydrated while exercising.

When should I refer to my GP?

If you have not passed urine for more than 8 hours, you feel light headed or lethargic, are suffering confusion or have a rapid pulse rate, refer to your GP or healthcare practitioner. You may also wish to consult your GP if you have been experiencing consistent thirst, because this can be a symptom of a chronic health condition, such as diabetes.

Now read...

How to eat in a heatwave
How to stay hydrated while exercising
More health & nutrition tips


This article was last reviewed on 16 September 2019 by Kerry Torrens.

Kerry Torrens BSc. (Hons) PgCert MBANT is a Registered Nutritionist with a post graduate diploma in Personalised Nutrition & Nutritional Therapy. She is a member of the British Association for Nutrition and Lifestyle Medicine (BANT) and a member of the Guild of Food Writers. Over the last 15 years she has been a contributing author to a number of nutritional and cookery publications including BBC Good Food

All health content on bbcgoodfood.com is provided for general information only, and should not be treated as a substitute for the medical advice of your own doctor or any other healthcare professional. If you have any concerns about your general health, you should contact  your local healthcare provider. See our website terms and conditions for more information.
 

Comments, questions and tips

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Brad West's picture
Brad West
8th May, 2019
Well done of having a nutritionist as the expert. So sick of "dietitians" posing as experts - any clown can set themselves up as a "dietitian" Nutritionist is the protected term and has to be studied for.
chrisnation's picture
chrisnation
7th May, 2019
150ml/day fruit juice? That's absurd. 150ml is the size of a single-serving yoghurt pot.
chrisnation's picture
chrisnation
7th May, 2019
6-8 glasses/day will do no harm to the vast majority of people, so the NHS is pretty safe in recommending it. However, the following is taken from an article on the same topic in The Times. "What is crucial here, however, is the word “fluid” because, physiologically speaking, this can be from any fluid source including tea, coffee, squashes, juices, diet or standard fizzy drinks and, to a certain extent, alcohol. Many foods provide fluids as well; watermelon provides 185ml (about a small yoghurt pot’s worth) of fluid per 200g slice. Even an average 100g banana provides about 75ml of water. Scientists say that there is no convincing medical research to prove that glugging litres of water on top of these needs will improve the elimination of toxins by your kidneys, improve skin tone or reduce your appetite or the frequency of headaches. Responding to your body’s thirst mechanism is apparently the best way to remain properly hydrated - and this goes for everyone, including those of us embarking on marathons and fun runs" So it seems the sensible thing to do is drink when you want to/feel thirsty. Tanking up with litres of unecessary water is pointless and simply jacks up the number of trips to the loo.
Robert Hind's picture
Robert Hind
13th Jul, 2018
But this ignores beer, wine and spirits. Sure, there is not a lot of water in a whisky and it tends to make you thirsty but beer is mostly water and it is easy to drink more than 2 litres during a normal evening in the pub !!
chrisnation's picture
chrisnation
7th May, 2019
Yes ... I have seen beer included, in responsible medical reports, as a source of hydration
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