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How to Stay Hydrated During a Triathlon Run

In this guide, we will explore on-the-run hydration strategies, covering tips and tricks for triathletes at various distances—sprint, Olympic, Ironman 70.3, and Ironman.

Know Your Sweat Rate

Understanding how much you sweat is essential for tailoring your hydration strategy. Weigh yourself before and after a training run to estimate your sweat rate. Each pound lost is roughly equivalent to 16oz/475ml of fluid.

Before your race you should ideally do a sweat test for the bike and the run as you will have a different sweat rate for each leg. Aim to do the sweat test at the beginning of training and then close to your event replicating race temperature and race conditions. This will help you plan your hydration during training and on race day.

You don’t need to go to a laboratory to do this, you can do this at home easily. Here’s how to do a sweat test. Once you have completed the test you can use this handy calculator to work out your sweat rate and how much hydration you need.

In cool conditions, or when you will only be sweating lightly, up to 500ml (16oz) of fluid should be sufficient for most people.

In warmer conditions and/or when you will be sweating more heavily, up to 750ml (26oz) might be needed.

In very hot or humid conditions and/or when you’ll be sweating a lot, you may find you need as much as 1 litre per hour of activity. It’s important to consider that approximately 1 liter (32 ounces) per hour represents close to a person’s the maximum absorption capacity during intense exercise. Trying to consume significantly more than this may not yield additional benefits unless your past experiences suggest otherwise.

Electrolyte Balance

Sweating not only expels water but also essential electrolytes. Replenish sodium, potassium, magnesium, and calcium with electrolyte-rich drinks or supplements to prevent cramping and fatigue.

Find out what works for you but if you do opt for supplements or hydration products then make sure they are batch tested. You can check your selected product here at the Informed Sport website.

Hydration is all about balance.

Everyone knows that being dehydrated can lead to poor performance and so athletes can focus on this and can in fact over-hydrate. Over consumption of fluids before and during events is common.

But being over-hydrated is potentially very dangerous.

It can lead to a condition called hyponatremia, which is caused by the dilution of the body’s electrolytes when too much fluid is taken in during a short period of time. Left unchecked, hyponatremia can be fatal. Sadly, it has killed several competitors in marathon and triathlon events. Even if it doesn’t kill you, a mild case of hyponatremia can ruin your race, through debilitating symptoms like headaches, lethargy, cramps, and sickness.

The aim of your hydration strategy is to achieve an optimal balance of fluids and electrolytes before getting to the start line. You then want to take in just the right amount of fluid and electrolytes during the race to minimise the negative effects of dehydration without over-doing it and running the risk of dilution and hyponatremia.

Trial and Error during Training

Experiment with different hydration plans during training to identify what works best for you. Factors such as climate, intensity, and personal tolerance vary, so find the right balance of water and electrolytes.

Find out what hydration is on the run course at your race and get some of that product to see if it could work for you. Try it out on a few long runs to see if it causes you gastrointestinal issues or even if you like the flavor!

You could make your own electrolyte or energy drinks, so you know exactly what goes into to them.

Portable Hydration Solutions

On the run leg of your triathlon on race day there will probably be water and electrolyte drinks on the course, but these can run out (if this happens it’s usually the energy drinks that run out rather than the water). For longer runs then taking hydration with you is a good idea both in training and on race day. Here are some popular ways to carry your hydration on the run in a triathlon.

How Much to Drink by Triathlon Distance

Sprint Distance (750m swim, 20km bike, 5km run)

Hydration’s more important for a sprint than fuelling, especially if you are racing in hotter conditions. So, sip 5-7ml/0.169-0.237oz fluid per kg of bodyweight.

For an 80kg/176-pound athlete, this equates to 400-560ml/13.5-19oz of fluid, which you can measure out in a water bottle. Focus on electrolytes to replenish lost minerals, including sodium. Racing up to 90mins means, technically, you don’t really need to fuel during your race.

  • Hydration Focus: Quick sips during the run.
  • Recommended Fluid Intake: 5-7ml/0.169-0.237oz fluid per kg of bodyweight.
  • Recommended Electrolyte Intake: Consider a balanced electrolyte drink if you require it.

Olympic Distance (1.5km swim, 40km bike, 10km run):

  • Hydration Focus: Consistent sipping to maintain energy levels.
  • Recommended Fluid Intake: 16-24 ounces per hour so around 2.6-4 ounces every 10-15 minutes.
  • Recommended Electrolyte Intake: Incorporate water and electrolyte-rich drinks.

Ironman 70.3 (1.9km swim, 90km bike, 21.1km run):

  • Hydration Focus: Regular and strategic hydration throughout the run practiced in training.
  • Recommended Fluid Intake: Typically, 50g carbs per hour, 700mg sodium per hour and an increase in fluid intake rate from 500mL/hr to 700mL/hr. Adjust to your training experience and race day conditions.
  • Recommended Electrolyte Intake: Utilize water and electrolyte drinks and adjust based on personal needs which you have tried and tested during your training.

Ironman Distance (3.8km swim, 180km bike, 42.2km run):

  • Hydration Focus: Sustained hydration to combat extended exertion and race day conditions.
  • Recommended Fluid Intake: Based on sweat loss; maximum absorption at 32 oz. or 1 Liter per hour. Sodium – 500-700 mg per Liter (or 32 fl. Oz). Optimal range is 4–8% percent carbohydrate for energy drinks. Concentrations higher than 8% may impede gastrointestinal (GI) emptying and cause gastrointestinal distress. If the concentration of carbohydrate is higher than 8%, water can be added to dilute it.
  • Recommended Electrolyte Intake: Prioritize electrolyte-rich nutrition, manage water and salt intake.


On-the-run hydration is a dynamic aspect of every triathlon, requiring careful planning and a willingness to adapt.

It’s essential to complete a sweat test for the run and test out your hydration strategy during training and on your long runs under race conditions.

Triathletes must be tuned into to their bodies, understanding the unique demands of each race distance.

By integrating effective hydration strategies that you have tried on your long runs and brick sessions during training, you will not only enhance performance but also ensure a more enjoyable and successful triathlon experience.

On-the-Run Hydration FAQ for Triathletes

How much water do I need during a triathlon?

Your water needs depend on factors such as distance, climate, and personal sweat rate.

In cool conditions, or when you will only be sweating lightly, up to 500ml (16oz) of fluid should be sufficient for most people. In warmer conditions and/or when you will be sweating more heavily, up to 750ml (26oz) might be needed.

What about electrolytes?

Electrolytes are crucial for preventing cramps and maintaining performance. Consider electrolyte-rich drinks or supplements. Experiment during training to find the balance that works for you.

Should I carry my own water, or rely on aid stations?

It depends on the race distance. For sprints, handheld bottles or on course water may suffice. For longer distances, consider a hydration pack, belt, or front-carry system. Aid stations can be a backup, but self-sufficiency is key.

Are there specific hydration considerations for each triathlon distance?

Absolutely. For sprints, focus on quick sips; for Olympics, maintain consistent sipping; for Ironman races, plan sustained hydration. Adjust fluid and electrolyte intake based on the race’s duration.

Can I rely solely on water, or should I use sports drinks?

Sports drinks can be beneficial as they replenish electrolytes. Experiment with both during training to determine your preference and tolerance. Some athletes prefer a mix of water and sports drinks for a balanced approach.

How do I carry hydration without it affecting my performance?

Choose a hydration method that suits your race distance and preferences. Handheld bottles, hydration packs, belts, and front-carry systems offer various options. Practice with your chosen method during training to ensure comfort.

What if I’m not thirsty during the run?

Thirst is not always an accurate indicator of hydration needs. Set a schedule for sipping water or sports drink, especially during longer races. Waiting until you’re thirsty may lead to dehydration.

Can I overhydrate? (hyponatremia)

Yes, overhydration, known as hyponatremia, can be dangerous. Monitor your fluid intake and balance it with electrolytes. Pay attention to your body and adjust your plan accordingly.

What are the signs of Hyponatremia?

Hyponatremia is a serious condition and occurs when the concentration of sodium in your blood is abnormally low. Sodium is an electrolyte, and it helps regulate the amount of water that’s in and around your cells.  

Symptoms include nausea and vomiting, headache, confusion, loss of energy, drowsiness and fatigue, restlessness and irritability, muscle weakness, spasms or cramps, seizures, and coma. In triathlon’s it can occur when you drink too much water making your sodium levels out of balance.

Are there any signs of dehydration I should be aware of?

Signs of dehydration include dark urine, dizziness, fatigue, and cramping. Stay vigilant, listen to your body, and adjust your hydration plan if needed.

How can I practice my hydration strategy before race day?

Train with the hydration methods you plan to use on race day. Experiment with fluid and electrolyte intake during long training sessions to identify what works best for you. Refine your strategy based on your experiences. Once you know your levels and what works for you create a race day hydration and nutrition plan. Don’t know where to start? Get in contact and I will help you,

On-the-run hydration is a personal aspect of your triathlon journey. Tailor your approach to fit your needs, and don’t be afraid to adjust your plan based on race conditions and individual responses.

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Joe is a collegiate swimmer who has been competing in triathlons for over 5 years, including sprint, olympic, and Half Ironman Distances. He loves open water swimming, lifting, and trail running as well.


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