Much of our body is made up of water (around 55-60%) so it’s no wonder that its an integral part of our health.

  • If you are a 91kg male then you are about 54kg of water.
  • If you are a 59kg female then you are about 33kg of water.

And if you are a baby then you are around 75% water.

Different cells contain different amounts of water:

  • Bone is about 22%
  • Adipose (fat) tissue is about 25%
  • Muscle and brain tissue are about 75%
  • Blood is about 83%
  • Eyes are about 95%

When do we need water?

As with everything, our bodies regulate thirst and will let us know when we require water.

We obviously get thirsty when:

  • Its warm
  • We’ve eaten something salty
  • We’ve drunk alcohol 
  • We’ve been sweating

There might be a bit of a delay between losing fluid and feeling thirsty.  Even a slight decrease in hydration can have an effect on our cognitive function and performance.

So how much water should you be drinking?

As a baseline, most adults require around 3 litres (12 cups) of water per day.  

If its warmer you may need an extra 500ml (2 cups) and if you are exercising you may need up to 6 litres (24 cups) per day

How do i calculate my basic fluid requirements?

For every kilogram of bodyweight, you should be ingesting 30-40ml of water.

This is just a baseline, obviously environmental and other factors will determine whether you require more or less.

The effects of water loss can have a detrimental effect on the body.

0.5% decrease can lead to increased strain on the heart.

1% decrease reduces aerobic performance.

3% decrease reduces muscular endurance.

4% decrease reduces muscle strength, motor skills & can cause cramps.

5% decrease can cause heat exhaustion, cramping, fatigue and reduced mental capacity. 

6% decrease can cause physical exhaustion, heatstroke, coma.

10-20% decrease can lead to death.

For most people just consuming plain water is fine, but for some athletes, its beneficial to drink sports drinks to help replenish their glucose & electrolytes.

For moderate activity under 2 hours and / or high intensity activity under an hour you should follow these guidelines:

  • Consume 0.5-1L (2-4 cups) of water during the activity.
  • Consume 0.5-1L (2-4 cups) of water after your workout
  • Consume 0.25-0.5L (1-2 cups) of water with each meal.

For moderate activity lasting longer than 2 hours and / or high intensity lasting longer than an hour you follow these guidelines:

  • Consume 0.25-0.5L (1-2 cups) of water 30-60 minutes before training.
  • Consume 30-45g carb + 15g protein + electrolytes (sodium and potassium) in 600ml of water every hour during activity.
  • Consume 30-45g carb + 15g protein + electrolytes (sodium and potassium) in 600ml of water afterwards.
  • Consume 0.25-0.5L (1-2 cups) of water with each meal.

If you follow these simple guidelines above you will be able to keep your body hydrated and perform at your best!


  • The Essentials of Sport & Exercise Nutrition by Precision Nutrition.

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