Keeping hydrated

Expert reviewer, Niamh Hennessy, Lead Dietitian, Bupa Cromwell Hospital
Next review due January 2024

You can’t survive without water – it’s essential for life. Your body is made up of mostly water. It makes up nearly two-thirds of a man’s body and just over half of a woman’s.

Water is important in your body – from removing waste products in urine, to lubricating your joints, transporting nutrients around your body and controlling your temperature. It can even help make your skin look good.

Here, we explain why you need to drink enough and share some tips on how you can stay hydrated.

Glasses of water with fruit

How much should I drink?

As a basic guide, most adults need about 2 to 2.5 litres of fluid a day. If a mug is around 250ml and a medium glass about 200ml, then that means drinking about 10 glasses or mugs of fluid a day. Children need less and pregnant women need a little more.

You get most of the fluid you need from drinks, but some comes from the foods you eat, such as soups, stews, fruit and vegetables.

You need to make sure the amount of fluid your body loses each day is replaced by the fluids you drink or get from food. This will stop you getting dehydrated. You lose about 1.5 litres of fluid a day when you pee, about 200ml in your poo and about 500ml when you sweat. You also lose fluid just by breathing.

The exact amount of fluid you need depends on things like:

  • Your age – as you get older your body stores less water and your kidneys don’t work as well as they once did.
  • The amount of physical activity you do – the more exercise you do, the more you need to drink.
  • The climate and your environment – you need to drink more if it's hot and you're sweating a lot or if you’re in a warm house or office with either central heating or air conditioning. Both air conditioning and central heating can dry the air.
  • If you’re pregnant or breastfeeding – you’re more likely to develop constipation, so you need to drink more.

Try keeping a water bottle with you and remember to sip on it throughout the day to help you stay hydrated.

What should I drink?

When choosing what to drink, think about the activity you’re doing and what your body needs. For example, if you’re doing light housework, a glass of water may be all your body needs to stay hydrated. But if you’re taking part in more demanding activity like running long distances and sweating a lot, you might benefit from a sports drink.

Any non-alcoholic drink can be part of the 2 litres or so that you’re aiming to drink every day. As well as giving you fluid, some drinks also give you vitamins and minerals.

When you’re choosing what to drink, it’s worth remembering that some drinks – for example, fruit juice – contain calories and sugar too. Drinks that contains lots of sugar can cause you to put on weight and increase your chances of developing type 2 diabetes. Sugary drinks can also cause tooth decay.


Water is a good choice when it comes to meeting your body's needs for fluids. It doesn't have any calories and is free if you drink tap water. If you’re not keen on drinking tap water on its own, you can filter or chill it or add sugar-free cordial. Sparkling or still bottled water works just as well as tap water at keeping you hydrated.

One way to make water more exciting is to add slices of lime, orange or lemon. Or you might like to add cucumber or berries to your drink. It gives the water a fragrance and taste that makes it much more interesting.

If you don’t like the taste of water to begin with, try to stick with it – the taste may grow on you over time. You could start by having a range of still, sparkling and mixed flavour waters until you get used to the taste.

Fruit juice and smoothies

Fruit juices and smoothies can contain lots of vitamins. One glass (150ml) can make up one of your five portions of fruit and vegetables a day. But they can contain lots of free sugars and acids, both of which are bad for your teeth. Because of this, it’s best to limit how much fruit juice you drink and to have it with a meal.

Remember that fruit juices and smoothies can only ever count as one of your five-a-day – even if you drink more than 150ml. If you buy fruit juice or smoothies, it’s important to keep an eye on the portion size because many bottles are larger than one 150ml serving. Try these top tips to help make your smoothies and juices hydrating.

  • Use crushed ice to thicken your smoothie rather than using yoghurt or milk.
  • Water-rich fruits include grapes, watermelon, kiwi and oranges, so these are good to add to your mix.
  • Water-rich vegetables for your green juices could include iceberg lettuce, cucumber and celery.
  • You can also use herbal teas like peppermint in your juices and smoothies.

Fizzy drinks

Fizzy drinks and squashes can contain more calories and sugar than you would imagine. Some fizzy drinks contain the equivalent of 12 teaspoons of sugar. If you can, choose no-added sugar, low-calorie, low-sugar, diet, light or zero versions of fizzy drinks and cordials.


Milk is a good choice because as well as water, it contains protein, B vitamins, iodine and calcium. If you can, choose semi-skimmed or skimmed options to keep the fat content low.

If cow's milk isn’t an option for you, plant-based milks such as soya, rice and almond milk are good alternatives for adults. Choose the unsweetened ones and look for those that have added calcium, vitamins and minerals.

Tea and coffee

Tea and coffee can be part of your fluid intake. Both have caffeine in them, which is a mild diuretic. That means they might make you pee more. If you stick to the recommended limits for caffeine each day, it shouldn’t affect how hydrated you are.

The recommended safe limits for caffeine are 400mg of caffeine a day for adults and 200mg a day for pregnant women. A cup of tea has about 50mg of caffeine in it and a cup of filter coffee has about 90mg. But the caffeine content can vary greatly between different products, so herbal teas or decaffeinated versions are also good alternatives.

Does alcohol count?

Although technically, alcoholic drinks contain water, they are also diuretics. This means they make you pee more and that can cause dehydration, especially if you drink a lot in one go. It's a good idea to drink water or other low-sugar or diet soft drinks alongside alcohol and to stay within safe weekly alcohol limits by drinking sensibly.

What about fluid in foods?

Some of the food we eat can also add to our daily fluid amounts. In fact, for every 100ml of liquid our bodies get each day, about 20ml usually comes from food. Foods like soups and stews contain a lot of liquid, but many fruits and vegetables do too. For example, melon and strawberries are almost all water. Even a banana, which you might not think has much liquid in it, is three-quarters water. Lettuce, tomatoes and cucumber are all around 95% water.

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It’s important to keep your body’s water content topped up, otherwise you could become dehydrated. If you’re not drinking enough or you’re losing lots of fluid, you can easily become dehydrated. Dehydration is when there’s not enough fluid going into your body to meet its needs.

So, how can you tell if you're dehydrated? There aren’t many signs that tell you when you’re dehydrated. One is feeling thirsty. But having a drink gets rid of the feeling of thirst before your body is completely rehydrated.

Another way to tell if you need to drink more is to look at how often you’re peeing and what colour it is. If you’re drinking enough, your pee should be pale yellow. If you don’t need to go as often as usual, you only pass a small amount each time and it's dark in colour, it’s likely that you’re dehydrated.

Some people may have a dry mouth and feel tired and dizzy.

Image showing hydration level by urine colour

What should I do if I become dehydrated?

If you think you may be dehydrated, start by drinking more fluid. For mild dehydration, drinking water or other drinks may be all that you need to do.

If you have more severe dehydration because of diarrhoea or vomiting, you’ll lose important salts and sugars from your body as well as water. If you’re older or have other health conditions, your doctor or nurse may suggest you use oral rehydration therapy. This is usually a powder containing sugar and salts that you mix with water.

If you think you may have severe dehydration, speak to your pharmacist straightaway.

Can you drink too much water?

You might have heard stories about people drinking too much water. It's certainly possible but it’s rare. Drinking a lot more than the recommended amount each day can mean your body isn’t able to get rid of the extra water fast enough. That can cause very low levels of salt and other important electrolytes in your body which can cause serious health problems So, it’s a good idea to drink no more than the recommended 2 to 2.5 litres a day.

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    • Personal communication, Niamh Hennessy, Lead Dietitian at Bupa Cromwell Hospital, April 2020
  • Reviewed by Sarah Smith, Freelance Health Editor and Michelle Harrison, Lead Editor, Bupa Health Content Team, January 2021
    Expert reviewer, Niamh Hennessy, Lead Dietitian, Cromwell Hospital
    Next review due January 2024