How much water do runners need?

Avoiding dehydration is key when running but it’s also important to avoid drinking too much, which in some circumstances can be fatal.

It is widely accepted that the average person needs 2 to 2.5 litres of fluid per day to allow the body to function normally. But not all that needs to come from drinks, with experts suggesting that at least a third of our daily fluid requirements are met by food.

We are all familiar with the well-known ‘2 liters a day’ or ‘8 glasses of water a day’ mantra. But does this apply to everyone, or is it too much or even, too little? Research suggests that drinking 2 litres of water a day, without fail, over and above other fluid intake is not necessary. Pretty much any drink at all — juice, milk, soft drinks and yes, even tea and coffee, can count towards the volume required. Caffeine is a diuretic, but the fluid provided in the drink is enough to offset its diuretic effect. Take 60mg of caffeine and add it to a cupful of water and milk, and you’ll likely end up more hydrated than if you hadn’t drunk it.

Fluid also comes in many forms — not just bottles and glasses. There is plenty of water in fruit, for example. If you ate a large slice of watermelon, you’d be taking a substantial amount of water on board, reducing the need to consume water in its pure form.

Water loss effects of running

Running necessitates a greater intake of fluid. Strenuous running can generate 20 times more heat than being at rest. We have to dissipate that heat somehow, to regulate and stabilize body temperature, and the body’s favoured method of losing heat is through sweating, which, of course, causes water loss. Without question, this also applies to any other type of fitness workout, particularly when in the form of high intensity interval training.

During a high-intensity workout, such as spinning or running, you could lose 500 to 1000ml per hour — and if this fluid isn’t replenished, dehydration will set in, causing a raised heart rate, increased blood pressure, a far higher rate of perception of effort, and ultimately, a decline in performance (even a dehydration level of 2 per cent can have a noticeable effect on your sporting prowess).

To account for fluid loss resulting from exercise, you need to think about drinking not just after training, but before and during the session, too. If you start your training session under-hydrated, you’ll be fighting a losing battle trying to compensate later. And guys be warned: research by world fitness organization IDEA shows that men are more likely to be dehydrated at the start of a workout than women.

Your hydration strategy should begin long before you start lacing up your running shoes — be aware of your food and drink intake throughout the day. Then consume 250 to 500ml of fluid 15 to 30 minutes before your running workout, depending on your tolerance of fluids, and the temperature and humidity. It doesn’t have to be all in one go.

During running exercise, aim to drink 100 to 200ml every 15 minutes. If you are exercising for an hour or more, isotonic sports drinks (Lucozade or Powerade, for example), containing electrolytes such as salt and potassium, as well as easily ingested carbohydrate and water, are more effective at delaying fatigue and enhancing performance than plain water.

Don’t leave it too late to rehydrate after running

In an ideal world, you would consume the same volume of fluid after a running workout that you lost through sweating, but studies show that replacing 80 per cent of what we’ve lost is a more achievable target. You can get a good idea of this volume through weighing yourself before and after a training session to see how much weight has been lost (yes, it’s all fluid — not fat!). More often than not though, this isn’t practical, so you need to follow some general guidelines about how much to consume.

When your running session is over, regardless of its length or intensity, drink at least 500ml of fluid. After a tough session, you may want to rehydrate with a sports drink, or a carbohydrate-rich fluid such as orange juice or fruit flavored concentrate. Another tried and tested tip of mine is to drink a glass of milk straight after exercise. Research has proven that milk can hydrate you far more efficiently than water, and also retain that fluid (i.e. you won’t be visiting the toilet all afternoon!). If you exercised for an hour or more, aim for a litre and keep drinking regularly for the next few hours until your urine is the colour of pale straw or lighter.

Over-hydrating before running

There’s been a lot of media coverage regarding the issue of drinking water during endurance running events, following a number of cases of ‘hyponatremia’, a potentially fatal condition in which the sodium concentration in the blood drops excessively due to too much water in the bloodstream.

The ‘drink, drink, drink’ message simply got interpreted a little too zealously and ended up causing some people to take on a lot more fluid than they needed. Research thus far suggests that women are more vulnerable to hyponatremia than men, probably due to their smaller body size.

To avoid being at risk of hyponatremia, try to consume isotonic drinks rather than water during endurance workouts or long runs, to prevent a drop in sodium — you could even try consuming a salty snack. And sip, rather than glug fluids down. It’s also a good idea to drink on a schedule — say, setting your sports watch to bleep every 15 minutes, rather than drinking unconsciously and unwittingly having too much.

Use your head when running

This all goes back to the phrase I use repeatedly on a daily basis — ‘listen to your body!’ Don’t go for a water strategy that’s going to leave you sloshing around like a waterbed. If you feel thirsty, then drink. If your stomach is already full, then don’t. When you feel hungry, is it really hunger pains or is it another way of your body telling you that you’re dehydrated? Hydrating yourself efficiently comes with huge benefits — your sleep will improve and you’ll aid your metabolism, you’ll be more alert, and it’s great for your skin! What more reason do you need than to reach for that next glass of the free stuff?!

Happy hydrating!