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Starting a run or race in a well-hydrated state is important. In the hours leading up to exercise, runners should drink regularly and adjust intake if they notice signs of dehydration, particularly in hot conditions or during heavy training periods.
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Hydration is one of the most talked-about aspects of running, but also one of the most misunderstood. How much you need isn't the same as the person next to you, and it can change depending on your training, environment and even your physiology. Age, gender, sweat rate, session type, duration, intensity and environmental conditions all influence hydration needs, which is why there is no one-size-fits-all approach. Instead of following generic rules, the goal is to understand your own needs and adjust accordingly.
How to tell if you're hydrated
Outside of a laboratory environment, one of the simplest and most effective ways to assess hydration is the WUT method, which stands for weight, urine colour and thirst as a part of the hydration testing method. If two of these indicators are off, it may suggest dehydration, and if all three are present, dehydration is likely.
For example, noticeable weight loss after a session, dark urine, and strong thirst together are clear signs that fluid intake needs attention. As a general guideline, limiting dehydration to around 2 to 3 percent of body mass helps minimise performance declines, particularly in hot or humid conditions, although this can be difficult to achieve in longer events such as marathons where sweat losses are high and fluid opportunities may be limited.
When hydration matters most
There are certain situations where runners need to be more deliberate with hydration. Running in hot or humid conditions increases sweat losses and makes it harder for the body to cool itself effectively. Altitude can also increase fluid loss through breathing and urination while simultaneously reducing thirst signals. Heat acclimatisation plays a role too, as runners who regularly train in warmer environments are typically better adapted than those coming from cooler climates. Even clothing can influence hydration by affecting how easily the body can dissipate heat during endurance training. Being aware of these scenarios allows runners to plan ahead and avoid unnecessary performance drops.
Common signs of dehydration
Dehydration does not always present dramatically at first, but there are some clear signs and symptoms of dehydration to watch for. These include mental and physical fatigue, nausea, light-headedness or dizziness, headaches, extreme thirst, and low-volume or dark-coloured urine. Recognising these signs early can help you adjust your intake before performance or recovery is affected.
Do you really need electrolytes?
Electrolytes, particularly sodium, are often marketed as essential for runners, but the reality is more nuanced. For most recreational runners, there is no strong evidence that additional sodium intake is required, as the body regulates sodium levels effectively through the kidneys and sweat glands. In addition, the higher food intake that typically accompanies training is usually enough to meet sodium needs through sport nutrition. What appears to matter more is the relationship between fluid and sodium rather than sodium in isolation. In most cases, a balanced approach to eating and drinking will meet requirements without the need for specific supplementation.
General hydration guidelines for runners
Before exercise
Starting a run or race in a well-hydrated state is important. In the hours leading up to exercise, runners should drink regularly and adjust intake if they notice signs of dehydration, particularly in hot conditions or during heavy training periods. A general guideline is around 5 to 10 ml of fluid per kilogram of body weight in the 2 to 4 hours before exercise. The choice of fluid can vary depending on conditions, with water, sports drinks or fluids containing electrolytes all being appropriate in different situations.
During exercise
Hydration during exercise is highly individual and is best practised in training. Ideally, runners should trial their approach in conditions similar to race day to better understand their sweat rate, gut tolerance and preferred fluid options.
For sessions under 60 minutes, water is usually sufficient. As duration or intensity increases, adding carbohydrates through sports drinks or other fuel sources may be beneficial. For longer sessions, a combination of fluids and nutrition can help maintain performance. In events lasting several hours, particularly in hot conditions, some sodium may support fluid retention and improve palatability, although for most runners this becomes relevant only in longer-duration efforts. Fluid temperature can also influence intake, with cooler drinks often easier to consume and colder fluids providing additional comfort in hot environments.
Recovery
After training or racing, the goal is to replace fluid losses and support recovery. A common recommendation is to aim for around 150 percent of fluid lost over the following 2 to 4 hours. This can be achieved through a combination of fluids and food, with options such as water, sports drinks, milk or smoothies all contributing.
Regular meals also support rehydration, as food naturally contains electrolytes. For most runners, there is no added benefit to supplementing electrolytes if adequate food and fluid intake is already in place. In situations where food intake is limited, including some sodium through fluids or snacks may help support hydration.
Keep it simple and individual
Hydration doesn't need to be complicated, but it does need to be personal. Understanding your own sweat patterns, training demands and environment will give you a far better outcome than following generic advice. For most runners, starting well hydrated, drinking to comfort during exercise, and replacing fluids afterwards is enough to support performance and recovery. If you are training or racing in more extreme conditions, or struggling to stay on top of hydration, working with a sports dietitian can help fine-tune your approach.
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Disclaimer
The information provided in this article is of a general nature only and is not intended to replace professional medical, health, or fitness advice. It does not take into account your individual objectives, physical condition, medical history, or needs. Before acting on any of the guidance or recommendations provided, you should consider whether it is appropriate for you in light of your personal circumstances. You should always seek the advice of a qualified healthcare professional (such as a sports dietitian or medical doctor) before starting, changing, or relying on any exercise, training, or nutrition program. Rebel Sport accepts no liability for any loss, injury, or damage suffered by any person relying on the information provided.
References
- Australian Institute of Sport. (2024). Electrolytes: AIS sports supplement framework [Fact sheet]. Australian Institute of Sport. https://www.ais.gov.au/__data/assets/pdf_file/0006/1001103/Electrolytes-Infographic.pdf
- American College of Sports Medicine. (1996). ACSM position stand: Exercise and fluid replacement. Medicine & Science in Sports & Exercise, 28(10), i–ix. https://doi.org/10.1097/00005768-199610000-00045
- Baker, L. B., De Chavez, P. J. D., Nuccio, R. P., Brown, S. D., King, M. A., Sopeña, B. C., & Barnes, K. A. (2022). Explaining variation in sweat sodium concentration: Effect of individual characteristics and exercise, environmental, and dietary factors. Journal of Applied Physiology, 133(6), 1250–1259. https://doi.org/10.1152/japplphysiol.00391.2022
- Casa, D. J., Cheuvront, S. N., Galloway, S. D., & Shirreffs, S. M. (2019). Fluid needs for training, competition, and recovery in track-and-field athletes. International Journal of Sport Nutrition and Exercise Metabolism, 29(2), 175–180. https://doi.org/10.1123/ijsnem.2018-0374
- Gatorade Sports Science Institute. (2024, July 15). Science of hydration. Gatorade Performance Partner. Retrieved January 5, 2026, from https://performancepartner.gatorade.com/resources/resource/science-of-hydration
- McCubbin, A. J., Allanson, B. A., Caldwell Odgers, J. N., Cort, M. M., Costa, R. J. S., Cox, G. R., Crawshay, S. T., Desbrow, B., Freney, E. G., Gaskell, S. K., Hughes, D., Irwin, C., Jay, O., Lalor, B. J., Ross, M. L. R., Shaw, G., Périard, J. D., & Burke, L. M. (2019). Sports Dietitians Australia position statement: Nutrition for exercise in hot environments. International Journal of Sport Nutrition and Exercise Metabolism, 30(2), 83–98. https://doi.org/10.1123/ijsnem.2019-0300
- McCubbin, A. J. (2025). Sodium intake for athletes before, during and after exercise: Review and recommendations. Performance Nutrition, 1, Article 11. https://doi.org/10.1186/s44410-025-00011-9
