What’s the best way to stay hydrated when exercising?

profile picture of Christina Merryfield
Senior Specialist Dietitian, Cromwell Hospital
04 January 2023
Next review due January 2026

Whether you’re an elite athlete or a weekend warrior, hydration is key during exercise. Here are some of our top tips to help guide you on how much you need to drink, and what to drink, before, during and after exercise.

woman running outdoors

Why is it important to stay hydrated while working out?

About half of your body is water, and it plays a vital role in bodily functions. You can lose a lot of fluid when you exercise  – as much as a litre or two an hour – mainly through sweating. So, you’ll need to drink more when you exercise to replace it.

If you don’t top this fluid back up, you can get dehydrated. This can affect both your general health and how well you exercise. You’ll feel tired if you’re dehydrated, and you won’t be able to control your temperature as well as usual.

If you’re dehydrated before you start exercising, your heart will also have to work harder to pump blood around your body. Staying hydrated means you can get the most out of your exercise session.

What are the symptoms of dehydration?

It can be hard to tell if you’re hydrated, especially because you might already be dehydrated by the time you feel thirsty. One quick way to test if you’re hydrated is to check the colour of your pee. If you’re hydrated, it should be pale and straw-coloured. If it’s darker, that means you’re probably dehydrated.

It can take time for fluids to be absorbed into your body. So, drink steadily during the day and aim to drink around 450ml of fluid in the two to four hours before you exercise. After that, drink more if you feel thirsty.

How much should I drink during exercise?

The amount you need to drink will depend on how much you sweat. How much you sweat is influenced by your:

  • size – larger people tend to sweat more than smaller people, and men sweat more than women
  • environment – you sweat more in hot, humid conditions
  • exercise intensity – you sweat more as you exercise harder

One way to know when to drink is to respond to what your body tells you. If you feel thirsty, you really need to drink as your body is already showing signs that it needs to take on more fluid. As a general rule, try to drink small amounts at intervals during exercise, if it’s practical.

Depending on how intense the exercise is, you should aim to drink about 120 to 240 ml of fluid. You can also work out how much fluid you need to replace by calculating your sweat rate. To do this, weigh yourself before and after exercise. As an example, if you lose one kilogram of body weight, you’ve lost approximately one litre of sweat.

What should I drink during exercise?

The array of sports drinks on the market can be overwhelming and they can contain lots of added sugar. But if you’re doing moderate amounts of exercise, such as a gym class, you’re unlikely to need them. Simple water is often the best thing to drink during and after a workout that’s shorter than an hour.

However, if you’re doing strenuous training or exercising for longer than an hour, sports drinks may be useful. As well as replacing lost fluid, sports drinks contain carbohydrates (sugar) and electrolytes (minerals like sodium and potassium), which you lose though sweat. These drinks provide fuel and help to keep you hydrated.

If you’re training for an endurance event like a marathon, you could speak to a registered dietitian or nutritionist specialising in sports nutrition for personalised advice. For more information, take a look at our guide on nutrition for sports and exercise.

Once all the hard work is over, no doubt you’ll be ready for something to drink. Not only will this be refreshing, but it will restore your fluid levels and aid your recovery. Drink small amounts of water regularly until your pee returns to a hydrated colour.

Don’t be tempted to reward yourself after exercise with a pint of beer or a glass of wine. Alcohol is a diuretic, which means it removes water from your body by increasing how much urine your kidneys produce.

Can you drink too much?

If you drink more fluid than you lose through sweating and peeing, this can cause a rare condition called hyponatraemia. Hyponatraemia can also happen if you sweat excessively without replacing electrolytes. If you have hyponatraemia, your sodium levels are low because your electrolytes have become too diluted. Symptoms of hyponatraemia include:

  • feeling bloated
  • a headache
  • feeling confused or disorientated
  • feeling sick or vomiting

If you have any of the symptoms above while you’re drinking during exercise, seek urgent medical advice.

Are you interested in learning more about your health? Discover more about our range of health assessments.

profile picture of Christina Merryfield
Christina Merryfield
Senior Specialist Dietitian, Cromwell Hospital

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