A runner drinking water during a marathon
© ©Virgin Money London Marathon

8 Tips to Perfect Your Marathon Hydration Strategy

Drinking the right amount of water is crucial to race success. But how much is too much? And what happens if you don’t drink enough? We asked an expert nutritionist for their advice.
By Howard Calvert
9 min readUpdated on
You’ve trained for months, feverishly following your schedule to the letter.
All the early morning runs in the dark when your bed seemed so tempting, and the increasingly long Sunday sessions have built up to this: the day you run 42km, a full marathon!
You’ve got your nutrition plan locked in place – you know your preferred brands, and what you plan on consuming both the night before and during the race.
But there’s one thing you might not have considered: hydration. Often, runners don’t think about it until the morning of the race. And considering that 83% of you is water, failing to prepare could make or break your run.
We asked leading sports and performance nutritionist Will Girling for his advice on how much liquid you should be taking onboard before, during and after the big event.

The minimum amount of hydration

A glass with measurements on it with a little bit of water

A glass with measurements on it with a little bit of water

© Steve Johnson / Unsplash

The biggest thing to keep in mind when trying to figure out the optimal amount of water to consume on race day is that it all depends on the individual person. There’s a conflicting amount of advice regarding how much water our bodies need and how much water we should drink day to day, but as a guide, Girling suggests 0.033ml/kg for the average person.
“Water requirements change based on each individual’s sweat rate,” says Girling. “This will also be affected by such things as heat, humidity and intensity of exercise. However, as a general rule of thumb, consuming 400ml to 800ml of water an hour should suffice.”
It can be tricky to calculate how much water you should consume during a marathon. Put a little thought into who you are as a runner and what race day will be like. For example, consider:
  • Your weight
  • How much you sweat
  • How long it will take you to finish the race
  • What the conditions will be during the race
From here, you can have a better sense of the minimum amount of water you’re going to need leading up to race day without over-hydrating. A good rule to follow is to try to consume around 400ml to 500ml 2 hours before the start and another 200ml 15 minutes before the run.
Then, make sure you continue to drink at regular intervals throughout the marathon.

Do the sweat test

Woman during a run

Doing a sweat test will help you perfect your hydration strategy

© Guido Mieth / DigitalVision / Getty Images

Girling says that you can perform your own sweat test to determine how much sweat you lose during an hour of exercise and, therefore, how much water you should be drinking to replace that.
Doing the sweat test allows you to dive deeper into the optimal amount of water to consume throughout the race. But there are still other factors and conditions to consider, like your running pace, the temperature, and your weight.
To do your own sweat test, follow these tips:
  • Weigh yourself before you run with no clothes on and make a note of it
  • Bring a controlled amount of water with you on your run, around 500ml will do
  • Run at a comfortable pace, or your typical race pace, for 60 minutes
  • Make sure you consume all the water you bring with you during your run
  • When you finish, undress, dry yourself off, and weigh yourself again
  • Make a note of the weight and compare it with the weight before you ran
“The difference in your weight will let you know your average sweat rate per hour at a race pace at that specific humidity and temperature,” says Girling.
Finding your sweat rate per hour can be helpful because you don’t want to lose more than 2 percent of your body weight during the race. Anything past this point without hydrating properly can lead to issues while you run – which you want to avoid, especially during a marathon.
Once you have your post-run weight, you can convert the difference into millilitres and then add it to the 500ml that you consumed while you ran to find your total fluid loss.
For example, if your weight difference was 0.5kg, you can convert this to 500ml and add it to the 500ml of water you consumed, totalling 1L of fluid loss.
Keep in mind that this will vary depending on the conditions you run in, so it can be worth conducting the sweat test in a few different conditions leading up to the marathon to have the most accurate picture.

The day of the marathon

Melbourne Running

Melbourne Running

© Riley Wolff

According to Girling, studies have shown that over-hydrating in the run-up to a marathon has proved ineffective. The best practice, he says, is to hydrate normally in the run-up to the day of the event.
Putting in some effort to stay hydrated in the 48 hours leading up to race day is often just as important as staying hydrated throughout the race itself.
“Start sipping about 600ml of water with an electrolyte tablet in it three hours before the race, and drink until your urine is clear. If it still isn’t clear, drink another 400ml on top of this.”
The 'check the colour of your urine' test is a reliable way to determine how dehydrated you are: the darker it is, the more dehydrated you are and the lighter/clearer it is, the more hydrated you are.
You don’t want to consume a large amount of water just before you start the race with the expectation that you will be hydrated for the entire time. If you do this, you run the risk of becoming bloated and messing with your sodium imbalance.
This is why it’s incredibly important for you to take the time to efficiently hydrate before you even get to the start line.

Don’t avoid caffeine

An overhead shot of a cup of coffee

An overhead shot of a cup of coffee

© Nathan Dumlao / Unsplash

“Tea or coffee does not dehydrate you in itself, but caffeine is a diuretic meaning it will cause you to pass urine more frequently,” says Girling. “So every time you go to the bathroom you should be topping up on water.”
But there’s more to your pre-run caffeine than just hydration benefits.
“Caffeine is proven in its performance-enhancing abilities. I would recommend 3mg/kg/bodyweight 30-60mins prior to the event. Though check this with your GP if you have any reason to be wary of high caffeine intakes.”
Even though consuming tea or coffee can bring positive effects and benefits, you also don’t want to overdo it. Make sure you drink the optimal amount around an hour before the race starts. This way, you can ensure you have time to go to the bathroom if you need to and you also have time to replenish the water you might have lost.

Try to acclimatize to the race-day weather

Runners standing in front of two fans to cool down after a marathon

Runners standing in front of two fans to cool down after a marathon

© ©Virgin Money London Marathon

With many races, the weather can prove tricky to predict, as 2018’s hottest London Marathon on record showed. “Running regular sessions at race pace will help to ensure you’re acclimatised,” says Girling. “But if it’s hotter on the day, understand that your fluid requirement will alter with an increased sweat rate.”
This is also going to work in a similar way if the weather on the day of the race is going to be a bit colder. You might not sweat as much compared to a sweltering hot day, but it’s worth exploring how to properly hydrate your body depending on what the temperature and climate will be.

Electrolyte balance is crucial

A lack of electrolytes can cause fatigue, dizzyness or worse

A runner with his arms around two volunteers helping him stand up

© ©Virgin Money London Marathon

There are multiple signs of dehydration and overhydration, with hyponatremia – where your blood's sodium levels are too low – being a condition that can be caused both by having too much fluid or not enough.
"The main issue is electrolyte balance,” says Girling. “It can cause fluid movement into the brain, causing swelling with symptoms that can progress from feeling strange, to mental confusion, general weakness, collapse, seizure, coma and, ultimately, death.”
One sign to look out for is your heart rate rising 5-8 bpm for every 1% of dehydration.
It’s incredibly important to take on electrolytes while running.
“Water on its own doesn’t hydrate you as well as it does if it contains electrolytes, but hyponatremia only happens with excessive water intake and no electrolyte intake, which upsets your body’s balance and you essentially dilute yourself,” says Girling.
“You can get your sodium loss rate tested, but if you’re leaving salt lines on your face or clothes you are likely to be a salty sweater.” Girling recommends 0.5 to 0.7g/l of sodium for exercise lasting less than three hours, with longer durations requiring more. Average electrolyte tabs are around 0.4g.

Make sure you grab some energy drinks, too

Most long-distance runs will hand out energy drinks along the route

A person handing out Red Bull cups to runners during a race

© [unknown]

As well as providing electrolytes, energy drinks provide carbohydrates, which help replenish glycogen stores (which generally run out after two hours of exercise), meaning you can maintain blood glucose levels and avoid 'hitting the wall'.
“Performance improvements have been seen from as little as 20g [or carbohydrates] an hour,” says Girling. “I would suggest aiming for 40-60g an hour at least, and more if you’re running intensely. Getting this from a glucose-fructose mix at a 2:1 ratio will improve your ability to digest it and reduce the chances of gastrointestinal distress.”

Keep drinking after the race

You don’t always have to live by the “drink when you’re thirsty” rule.
“Typically, if you’re drinking when you’re thirsty, it means you’re already a bit dehydrated,” says Girling. “Steady consumption of liquids matched with your hydration testing, and ensuring that you’re not losing more than 2% bodyweight, should be the focus.”
Drink water with electrolytes for a while after the event

A runner outside on a sunny day drinking water from a water bottle

© RICOWde / Moment / Getty Images

Most marathons will supply 250ml bottles, so you can keep an eye on exactly how much water you are drinking.
On reaching the finish line, your marathon effort is over, but your hydration strategy isn't (just yet).
When you reach the finish line, your marathon effort is over but your hydration strategy isn't – not yet, anyway.
“Ensuring you’ve replaced what you’ve lost should be the main goal after finishing, so continue to drink water with electrolytes for a while after the event,” says Girling.
Running a marathon is no doubt going to strain your body and put it into overdrive. There is constant pressure on different joints, you use up all of your energy stores, and your muscles slowly begin to break down.
This is why continuing to hydrate once the race is over is important to help reduce the possibility of injury and muscle cramps, and aid in your overall recovery.

Running for sport, running for fun, and running for research

Everybody is going to be a bit different when it comes to implementing the right hydration strategy. It’s going to depend on things like experience, age, weight, and how long you’re running for.
Even when running for fun and for a good cause, staying hydrated will help you reach your goal – no matter what it is. The Wings for Life World Run happens each year and is in support of finding a cure for spinal cord injury.
The good news? You can take part in the race regardless of where you are. To find out more and sign up for this year's run, check out the Wings for Life World Run website.

3 min

Best moments from the Wings for Life World Run 2023

Hundreds of thousands people worldwide raced to support cutting-edge spinal cord research. See the highlights.


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Wings for Life World Run

The world's biggest running event connects runners and wheelchair users globally with a fun, unique format and compelling charitable objective: 100 percent of entry fees go to spinal cord research.

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