How Much Water Do I Need When Exercising?

If you don’t keep your hydration levels up when exercising, your performance will suffer.  Without getting enough water into your body to replace the sweat you lose, you’ll struggle to get cool, and risk overheating which can be dangerous.

There’s a common myth that you need to drink 8 glasses of water each day, but in truth, it doesn’t appear that there’s ever been a proper scientific study that proves that 2 litres is in some way the magic number for everyone.

The amount of water you need when exercising depends on a number of different factors:

  • The type of exercise
  • Your weight
  • Your fitness level
  • The ambient temperature and humidity
  • What you’ve eaten that day

If you weigh 200KG and go running on a hot dry day, you need a lot more water to replace sweat and keep your body temperature stable than a 100KG person who is lifting weights in an air conditioned gym.


In most cases, simply being thirsty is an indicator that you need to drink something.  Our bodies generally tell us pretty quickly that they need water – scientific studies suggest that the thirst response kicks in when our blood concentration increases by just 2-3%!

When you’re exercising, you need to drink enough water to replace the water that you’re losing from your system as sweat.  The hotter you get in your workout, the more you will sweat, and the more you will need to drink.

Ideally, you want to maintain a fairly even level of performance throughout your workout session, which means keeping your body hydrated at a consistent level.  Taking a 500ml bottle of water on your run and sipping regularly as you go should be fine for a run of up to an hour.  Any longer, and you might want to consider investing in a backpack, or a water belt to keep you going.