How to stay hydrated during a full distance triathlon

Chief Correspondent

Andy Blow has a few top-10 Ironman and 70.3 finishes and an XTERRA World Age-Group title to his name. He has a degree in Sport and Exercise Science and was once the Team Sports Scientist for Benetton and Renault F1 teams, working with Jenson Button.

He founded Precision Hydration to help athletes solve their hydration issues and has personalised the hydration strategies of a long list of elite triathletes.

Over the summer he’s been writing a series of articles on hydration for us, including advice on how to stay hydrated during short course and middle distance races.

This post covers how to stay hydrated during full distance races, just in time for the Ironman World Champs in scorching hot Kona, Hawaii…

How to stay hydrated during a full distance triathlon

During long distance racing the potential for race-ruining hydration issues is very high – especially when you’re racing in the hot conditions found in races such as Kona –  so it’s well worth giving some proper thought to what fluid and electrolytes you might need to take in to minimise the chances of all of your training going to waste…

What to do before a full Ironman race

Drinking a strong electrolyte drink to boost your hydration status before a race can really improve your performance.

This is known as “preloading” and it’s especially important before full distance triathlons because starting fully hydrated gives you a bigger reserve of fluids and electrolytes to draw upon once the race begins. Essentially, it’s all about getting you to the start line ready to perform at your best.

One easy way to get more sodium in before a race is through an electrolyte supplement, but just make sure it’s strong enough to make a difference. Most electrolyte supplements you’ll have heard of contain less than 500mg of sodium per litre, which is only about half the amount the average triathlete loses in their sweat.

  • Drink a stronger electrolyte drink (like PH 1500) with 500ml/16oz of water the evening before your race. Drink this with water you’d have drank anyway to ensure you don’t overdo it.
  • Drink another strong electrolyte drink (like PH 1500) with 500ml/16oz of water a few hours before you anticipate getting into the water.
  • Finish your drink at least 45 minutes before you start to give your body time to fully absorb what it needs and pee out any excess.
  • DON’T just drink lots of water in the build-up to a race. You can end up diluting your body’s sodium levels before you start, increasing the risk of hyponatremia.

If you’re getting your sodium in through food, aim for about 1000-1500mg of sodium per litre of water you drink alongside it. Remember that table salt is only 39% sodium (61% is chloride), so 1g of salt only gives you ~390mg of sodium.

Why “preloading” works

Boosting your blood plasma volume before intense exercise is a proven way to enhance your performance, especially in hot conditions. Having more blood makes it easier for your cardiovascular system to meet the competing demands of cooling you down and delivering oxygen to your muscles.

Stronger electrolyte drinks (containing at least 1,000mg of sodium per litre) are very effective at increasing your plasma volume as they contain more sodium than a typical sports drink. That extra sodium helps to pull water into your bloodstream and keep it there. For more on the research behind this pre-race advice, read this blog.

You can’t preload anywhere near as effectively with weaker sports drinks as you’ll lose a large proportion of the fluid as urine. Or, it’ll slosh around in your stomach without being properly absorbed.

What to do during your race


During the swim

If you’re drinking much during the first leg of a triathlon, you might need to work on your technique! If the swim’s in salt water, you might want a bottle of water by your bike so you can quickly swill your mouth out before jumping onto the bike, but that’s all really.

On the bike

The bike leg is the best time to get fluids and electrolytes on board because you can carry them easily and drinking is easier when riding than when running. This is crucial in long distance races as, if you start the run low on fluids or electrolytes, you could have a long and painful marathon ahead of you…

What electrolyte drink is right for you?

How much sodium you need to be taking in on the bike is determined by a few things…

  1. Firstly, everyone loses a different amount of sodium in their sweat, from as little as 200mg of sodium per litre of sweat to as much as 2,000mg/l. This is genetically determined.
  2. Sweat rates also vary from person to person of course; and from situation to situation.

When you combine differences in sodium concentration (ie how salty your sweat is) with those in sweat rates (how sweaty you are), the potential difference in the total net sodium losses experienced from one triathlete to another can be significant, especially over a long distance triathlon.

Photo by Joern Pollex/Getty Images for Ironman

Because sweat/sodium losses are so personal, any generic guidelines on the replacement of sodium and fluid should always viewed with suspicion. Having said that, figuring out whether your net losses are likely to be low, moderate, or high can be a great starting point for honing in on the level of sodium and fluid replacement that’ll work best for you in different circumstances.

At Precision Hydration, we’ve developed a free Triathlon Sweat Test that can help with this process.

How much should you drink on the bike?

Everyone is different, but here are some guidelines to help you hone in on what works for you…

  • During a full Ironman, you need to make a conscious effort to stay on top of your fluid and electrolyte replacement throughout the bike leg to avoid dehydration derailing your race later on. Hydrating effectively on the bike is about setting up a successful run and not just surviving to the end of the ride.
  • Few people can process more than about one litre (32 oz) per hour during the bike section, so that’s probably the upper limit of how much you’d need to carry (unless experience dictates otherwise). This is especially important to remember in Ironman because the risk of hyponatremia from drinking too much is greater than in shorter events.
  • Most athletes will need to take in between 600ml and one litre per hour during a long distance ride. The exact amount depends on the conditions, your own sweat rate and past experiences.
  • If you’re not drinking enough on the bike, you’ll probably feel thirsty, or have a dry mouth. Listen to your body and drink to the dictates of thirst. It can also potentially be a warning sign if you don’t need to pee once during the last third of the bike ride.
  • If you’re feeling bloated, can sense fluid sloshing around in your stomach, or you need to pee often during the race, then you may be drinking too much. You might pee 1-3 times during a full distance race, but much more than that could indicate you’re overdoing it.

Experimenting within these guidelines whilst learning to listen to your body is the best way to find out how much you need to drink during a race.

How to stay hydrated during a full distance triathlon (Photo: Richard Melik / Team Freespeed)
Photo: Richard Melik / Team Freespeed

During the run

How much should you drink on the run?

How much you’ll need to drink on the run in a full distance tri will be heavily influenced by the race climate, your pace, how much you’ve been sweating and how much you’ve managed to consume on the bike.

Most athletes find they can take in less fluid per hour on the run than they can on the bike, which should give you an idea of the kind of volumes you might be able to tolerate.

The extremes you’re trying to avoid are under-drinking to the point that dehydration hampers your performance, whilst not over-drinking, which can lead to hyponatremia.

Listening to your body to help guide how much fluid/electrolytes you take in is important here. It’s very hard to predict what state you’re going to be in when you hit T2, so being able to react to what your body is telling you is critical.

If you get really thirsty, then it’s a good idea to walk through some aid stations to ensure you get enough fluid on board. A few seconds lost doing this is better than getting very dehydrated later on and risking a DNF!

Carrying your own salt capsules with you to take with water picked up at aid stations is also potentially a good idea as you’re unlikely to be carrying fluids during the run.

Remember that dumping water or ice over your head at aid stations can also help with hydration when it’s very hot. The cooling sensation this triggers means your body has to sweat less to keep itself from boiling over.

How to stay hydrated during a full distance triathlon (Photo: Richard Melik / Team Freespeed)
Photo: Richard Melik / Team Freespeed

What to do after a race

Restoring hydration levels is a big part of the recovery process after you’ve been sweating a lot. Research shows that drinks containing sodium enable better rehydration as they allow your body to hold onto more of the fluid rather than peeing it out.

Most athletes finish an Ironman dehydrated to some extent. Research and our experience suggests that, in many cases, there’s nothing wrong with this. It’s better to finish a little bit dehydrated rather than with hyponatremia. A loss of 1-4% body weight is pretty typical for most people in normal scenarios.

I’d suggest mixing up a 500ml/16oz bottle or two of a stronger electrolyte drink (like PH 1500) to sip in the first few hours after you finish. Just drink as much as you feel you need to.

Janos M. Schmidt / ITU Media /

Hopefully this article helps as you start to personalise and refine your hydration strategy. Of course, it goes without saying that any tweaks to your hydration plan should be thoroughly tested in training first to iron out any kinks.

Best of luck in your next full distance race, especially if you’re reading this from the Big Island!

Train Hard.

John Levison
Written by
John Levison
Latest News
Gustav Iden on the run at WTCS Abu Dhabi 2023
Gustav Iden pens beautiful tribute after his mother loses her brave battle against cancer
Alex Yee & Alistair Brownlee
Is Alex Yee the heir to Alistair Brownlee’s throne? Inside the insane WTCS Cagliari numbers
Will McCloy
Raising triathlon’s broadcast standard: Will McCloy and Sub7Sub8
Leo Bergere finishes third at WTCS Cagliari
World Champion Léo Bergere beats ‘weird’ sensation to make podium return in Cagliari
IRONMAN Brazil 2023: Taccone and Oliveira win in Florianópolis