Water: the stuff of life

As it's the hottest week of the year so far, I thought it might be useful to give you some helpful hints and tips on water and staying hydrated. Hopefully something in here helps you to find your fluid balance.

How much fluid do you need?

Use this calculation to work out your base needs...

  • Age: up to 30 = 35-40ml of water per kg body weight (multiply your weight in kg by 0.035 or 0.04)
  • Age: 31-54 = 30-35ml of water per kg body weight (multiply your weight in kg by 0.03 or 0.035)
  • Age: 55-65 = 30ml of water per kg body weight (multiply your weight in kg by 0.03)
  • Age: 65+ = 25ml of water per kg body weight (multiply your weight in kg by 0.025)


So, for example, Bob is 56 years old and weighs 80kg, the calculation he needs to do is:

80kg x 0.03 = 2.4 litres per day


What about exercise?

The more exercise you do the more fluid you'll need. Hard exercise can increase your daily fluid needs by up to a litre for every hour done. Check out the tests later in this article to work out if you're getting the right amount for your needs.


What counts towards my fluid intake?

There's water in your food, so if you're eating a healthy, balanced diet, it's thought that around 20% of your basic water needs are met. So for our example above, Bob would be getting just under half a litre each day through food  and need to drink around 2 litres each day.


Drinks that count towards hydration include:

  • Water
  • Squash
  • Milk
  • Fruit juice (this will hydrate you but can be higher in calories so you may want to dilute it with water)
  • Fizzy drinks (yep even these hydrate you; again though they'll often be higher in calories so limit the amount you consume)
  • Tea and coffee (the vast majority of what's in your mug is water so it serves to hydrate you, outweighing the diuretic effects of the caffeine. If you're sensitive to caffeine you may want to limit the amount of coffee you drink to just a few each day)
  • Shandy (yep because there's very little alcohol in here, it can hydrate you. Too much booze though will dehydrate you, so either limit the amount or drink plenty of water at the same time)


How do I check that I'm getting the amount I need?

Every one of us needs a slightly different amount of fluid. Whilst the calculations above are helpful, you'll likely need to make tweaks to how much you drink based on:

  • Your genetics
  • Your training regime
  • Your diet
  • The weather
  • Illness
  • Age, gender, pregnancy, the number of diuretics like alcohol you've been cons,ing, sleep, stress and medication

Because of this, there are some great tests you can do to see if you're getting what you need:


1) How do you feel? Tiredness, dry mouth and skin, headaches, irritability, unusual hunger and aching muscles can all be signs that you're dehydrated. Listen to your body and if you think you're thirsty, drink fluids little and often to help rehydrate yourself.


2) The pee test. Urine should be light or straw-coloured. Darker urine or even only urinating a few times each day suggest you're dehydrated. The NHS suggests that going to the loo less than 3 or 4 times a day is a good sign.


3) For the exercisers out there, weighing yourself before and after training can be a great marker of hydration. Sadly if you've lost three pounds during your workout I'm sorry to say it won't all be fat! Much of it will be water and will mean you need to rehydrate. 

Even just a 1-2% decrease in weight after a workout will mean you are dehydrated and need to replenish your fluids. If not you may feel unwell, tired and your exercise and mental performance can decrease significantly.

Just as an example of how small a weight loss this can be, for me, weighing in at 70kg, even a loss of 0.5-1.5kg (1-3 lbs) after a session means I'm dehydrated. This would likely need me to drink somewhere between 0.5 and 1.5 litres of fluid to replace these losses.



Drink little and often across the day using any combination of the drinks outlined. Monitor your hydration levels through how you're feeling, your urine colour and your weight post-exercise.

Over time you'll learn the timings and amounts that work for you to maintain your fluid balance.