How Much Water Should You Drink to Stay Hydrated?

The '8 glasses a day' myth gets busted

We've all heard the advice, "drink at least 8 glasses of water a day" to stay hydrated and healthy. In fact, you’ve probably heard it as many times as you’ve been told to look both ways before your cross the street or brush your teeth before bed.

However, according to Andy Blow, co-founder and Sports Scientist at Precision Hydration and a  Red Bull High Performance partner, this rule that everyone and their mother loves to tout is probably not the best guide for achieving optimal hydration.

"It's a bit like the 'how long is a piece of string' question. It depends a lot on your size, activity level, sweat rate and so on. The range of potential fluid requirements amongst people is huge," says Blow.

In other words, everyone's fluid requirements are different and the amount of water you should drink on a daily basis depends on a range of individual factors. But if this is true, then how can you figure out an appropriate amount to drink?

"I think what it is best to say is that if you largely drink according to the dictates of thirst, and try to make sure the vast majority of your fluid intake comes from water you won't be very far wrong," says Blow.

He also recommends adding more fruits and vegetables to your diet because of their high liquid contents.

"If you can include a lot of these into your regular diet you will be doing your hydration levels a favor, as well as your general health," he says.

When it comes to athletes and avid exercisers, Blow says that even though most are primarily concerned with avoiding dehydration, over-hydration is actually a much more common problem.

"This can be especially problematic if athletes drink excessive amounts of low sodium fluids over several hours, usually immediately before and during an event, and end up diluting the levels of sodium in their blood," says Blow "If it goes unchecked, this can result in hyponatremia, a potentially deadly condition where the brain swells due to having to absorb excess fluid from the blood."

The best way to avoid over-hydrating is simply to drink to thirst. If you're getting ready for a big event or an intense training session you can increase your fluid intake slightly.

"In the final 48 hours before events and big training sessions we advise a lot of athletes to increase their fluid intake by an extra 500-750ml or so on top of their normal intake with some extra sodium in it to help the body absorb more of this additional fluid without diluting the blood," says  Blow.

This is the third installment of our three part series on hydration featuring the expert insight of Andy Blow, co-founder and Sports Scientist at Precision Hydration and a Red Bull High Performance partner.

Part 1: How Often Should You Rehydrate During Exercise?
Part 2: Do You Need to Replenish Electrolytes After Exercise?