How to drink water during a workout

Posted by
Lauren Clark
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Do you sometimes experience nausea and fatigue when you work out? It could all be due to that trusty bottle of water you’re gulping down so diligently…

A lot of thought goes into packing the average gym bag. Feather-light trainers? Check. No-budge leggings? Yep. Favourite hair tie? Natch. But one workout accessory that we tend to pay little attention to could actually help us achieve that PB. Our water bottle.

Stay with me here. Surely we know how to stay hydrated as we exercise? But it turns out it’s more complex than just downing an entire bottle when your throat feels like the Sahara. 

From the litre bottle brigade to the class latecomers who are forever “just nipping to the fountain”, many of us are running the risk of both nausea-triggering gulping or dehydration-related fatigue. Paying more attention to how fast you rack up those millimetres, and when, is key.

But first, why does H20 become incrementally more important the moment we pass the warm up? “It helps you perform your best,” says Anita Bean, a registered nutritionist and author of The Runner’s Cookbook, who credits water with preventing reduction in intensity and stamina, and a drop of endurance by as much as 10 to 20 per cent. Plus, dehydration can leave you dangerously dizzy and uncoordinated.

However, before you begin downing water like it’s going out of fashion, she points out that you’re not a never-ending reservoir. “Many people don’t realise that the body can’t cope with more than 800ml in a short space of time as that’s the maximum your stomach can take,” warns Bean, who points towards that annoying mid-workout toilet break.

What’s more, different gym workouts require more hydration than others. “A gentle weights session may need just a 400ml top up, while a very intense HIIT class could demand something closer to the 800ml mark,” explains Anita. 

For workouts of under 30 minutes it is unlikely you’ll need to take on any extra fluid at all, while marathons will require you to be more specific and replace around 80 per cent of the sweat weight you naturally shift. For any workout you can calculate how much water you lose by hopping on the scales before and after.

That’s the thing, how much water you actually need in your bottle is very individual. It can be influenced by everything from the weather, to whether you crank up the resistance on that spin bike, and how sweaty you tend to get. The American College Of Sports Medicine recommends everyone listens to their body primarily and drinks to thirst.

Some even suggest sipping ahead of it. “If you’re dying for water, it’s too late,” says Neville Kenwright, trainer at F45 Fulham and DUO Chelsea. Others stress the importance of staying hydrated throughout the entire day surrounding a workout.

But while the debate rages on, experts agree that gulping water continually throughout a session will do you no good. “Sipping water at 15 to 20-minute intervals is by far the best way,” says Luke Hughes, a trainer with background in sports science, who founded Origym. “This prevents vomiting, gagging and stomach discomfort,” he says.

It also reduces the risk, according to Andy Vincent, a trainer at Third Space, of potentially-fatal hyponatremia, where too much water in a short space of time causes sodium levels to drop dangerously low.

The only exception to gulping, says Bean, is if you’re slightly dehydrated at the start of class and need to get fluid on board quickly. “Those three to four gulps - around 150ml - will be absorbed reasonably fast if your body needs it,” she says, who advises using the good old ‘toilet test’ to check that your urine is an optimal pale, straw colour and no darker.

Experts also agree that pure water really is all you need for a sweat session running under 90 minutes. Luke Worthington, trainer at FIIT, suggests that topping up on electrolytes, which can be found in bananas and coconut water, could also help boost hydration, but insists that supplementing with Branch Chain Amino Acids (BCAAs) is a waste of money. As is investing in a pricey water bottle. “Choose whichever refillable water bottle is most comfortable for you,” he says.

So the next time you’re assembling your gym bag, maybe give that water bottle the attention it deserves.

A step-by-step guide to workout hydration…

1. Don’t drink the moment you step into class

“Ask yourself if you really are thirsty yet, otherwise hold off,” advises Anita Bean. “You shouldn’t force yourself to drink.”

2. However, if you think you might be slightly dehydrated, drink little and often

“Take three to four generous sips - around 150ml - every 15 minutes to get your hydration levels back on track,” says Anita.

3. Drink within the first 30 minutes of a session

“If you’re working out for an hour or longer you should start sipping within the first half an hour,” recommends Anita. “It takes approximately 15 to 30 minutes for the water to reach your cells.”

4. If you don’t tend to sweat or get thirsty, don’t go entirely without

“Try and take in even a small amount of water every 20 minutes or so,” says Andy Vincent.

5. Don’t drink too much towards the end of your workout

“It takes 45 minutes to fully rehydrate,” notes Neville Kenwright. So there’s no need to go overboard close to cool down.

Three water bottles that tick the PTs’ boxes…


Andy Vincent recommends BPA-free bottles that you can chuck in the dishwasher.


“Glass bottles tend to give off less of a taste than plastic versions,” says Luke Worthington.


“Get a bottle with millimetre markings on the side so you can keep an eye on how much you’re drinking,” recommends Luke Hughes.