Hydration Strategies for Marathon Running: A Practical, Science-Based Guide for Runners of All Levels

Running a marathon is a major physical undertaking that tests both endurance and mental resilience. One crucial yet often misunderstood aspect of marathon preparation and performance is hydration. Whether you’re lacing up for your first 26.2 miles or aiming for a personal best, a solid hydration strategy can mean the difference between hitting the wall and crossing the finish line strong.

This article explores hydration from a sports science perspective, offering evidence-based strategies tailored to beginner, intermediate and advanced runners. Practical takeaways are included to help you hydrate intelligently, using the latest peer-reviewed literature to support your training and race-day approach.

Why Hydration Matters in a Marathon

Hydration during endurance running is not just about drinking plenty of water. It’s about maintaining fluid balance and avoiding the dual pitfalls of dehydration and overhydration. Both can significantly impair performance and potentially lead to serious health consequences.

Dehydration, defined as a loss of more than 2% of body weight due to fluid loss, can reduce endurance, increase core temperature and heart rate, and impair mental function (Cheuvront & Kenefick, 2014). Conversely, overhydration – or exercise-associated hyponatraemia (EAH) – occurs when sodium levels in the blood become dangerously diluted, often due to excessive water intake (Hew-Butler et al., 2015).

Modern hydration guidelines advocate for personalised strategies based on individual needs rather than a one-size-fits-all model (Sawka et al., 2007).

Hydration Strategies by Experience Level

Beginner Runners: Laying the Foundations

As a new marathon runner, your main goal should be to develop a simple, consistent approach to hydration that works for your body.

1. Drink to thirst

Rather than forcing fluids, beginners should focus on drinking when thirsty. The “drink as much as possible” mantra has been replaced by a more cautious, physiology-based model (Noakes, 2007). Your body is generally a reliable guide.

2. Pre-run hydration

Consume 5–7 mL of fluid per kg of body weight about 4 hours before a run (Sawka et al., 2007). If urine remains dark or output is low, an additional 3–5 mL/kg may be consumed 2 hours before exercise.

3. During the race

Aim for 400–800 mL per hour, adjusting for temperature, effort and sweat loss (Armstrong, 2021). This prevents both dehydration and excessive intake.

4. Include electrolytes

Sweat contains more than just water – it also includes essential electrolytes, especially sodium. Using sports drinks or electrolyte tablets helps maintain fluid balance (Shirreffs & Sawka, 2011).

Practical tips for beginners:

• Test hydration during long training runs.

• Choose drinks you’ve used before to avoid gastrointestinal distress.

• Monitor your urine colour – pale yellow is the goal.

• Use aid stations sensibly – sip, don’t gulp.

Intermediate Runners: Refining Your Approach

As a more experienced runner, you may want to personalise hydration based on your physiology and race-day demands.

1. Know your sweat rate

You can estimate your sweat loss by weighing yourself before and after a one-hour training run (in similar conditions to race day), adjusting for any fluid consumed. The change in weight reflects your sweat loss, which helps tailor your intake (Cheuvront et al., 2007).

2. Consider preloading with sodium

Drinking a high-sodium beverage (~1,000–1,500 mg/L) the night before and morning of a marathon can increase plasma volume and reduce the risk of cramping or early fatigue (Maughan & Shirreffs, 2008).

3. Fuel and hydrate together

Combine fluid intake with carbohydrate consumption – around 30–60 g of carbohydrate per hour – to maintain energy stores. Many sports drinks and gels are designed to deliver both.

4. Adjust for the environment

Humidity, heat and altitude all influence fluid requirements. Be proactive on warmer days and reduce intake slightly in cooler conditions.

Practical tips for intermediate runners:

• Create a hydration schedule for race day based on training.

• Use a mix of fluids and gels to cover both hydration and energy needs.

• Try salt capsules if you have a history of cramping or heavy sweating.

Advanced Runners: Optimising for Performance

Elite and experienced runners often take a data-driven, individualised approach to hydration.

1. Use lab testing (if available)

Some athletes benefit from sweat composition analysis, which determines the concentration of sodium lost in sweat. Products like Precision Hydration offer tools to match electrolyte needs with appropriate supplements.

2. Avoid overhydration at all costs

EAH is more common in slower runners who drink excessively due to fear of dehydration. However, elite runners can also fall victim if they drink habitually, rather than to thirst. Use body mass changes post-race as a metric – a loss of more than 2–3% may indicate underhydration, while no change or gain suggests overhydration (Hew-Butler et al., 2015).

3. Pre-race simulations

Run training sessions at race pace under race-like conditions. This helps identify gastrointestinal issues, refine fuelling, and understand how much fluid you truly need.

4. Real-time monitoring

Advanced runners might use wearable tech that tracks sweat rate, skin temperature and hydration status. While not essential, such tools offer insights that can fine-tune your plan.

Practical tips for advanced runners:

• Calculate fluid needs based on actual data.

• Choose drinks and supplements tailored to your sweat profile.

• Make adjustments mid-race if conditions or your pace change.

General Advice for All Runners

Regardless of experience level, the following recommendations apply:

• Avoid last-minute changes. Stick with the hydration routine you’ve practised in training.

• Pair hydration with fuelling. Carbohydrates and electrolytes improve fluid absorption.

• Use aid stations wisely. Know where they are and what they provide.

• Don’t fear dehydration. Mild dehydration (up to 2% body weight) is not harmful and may be optimal for some (Noakes, 2007).

Post-Race Rehydration

After the marathon, focus on replenishing fluids, sodium and glycogen stores. Aim to drink 1.25–1.5 times the fluid lost, ideally containing sodium and carbohydrates to speed rehydration (Shirreffs & Maughan, 1998).

Conclusion

Hydration for marathon running is as much an art as it is a science. There is no perfect number of millilitres per hour that suits everyone. The key is to listen to your body, practice in training, and adjust based on evidence and experience. Whether you’re a beginner just hoping to finish, or an advanced runner chasing a PB, a tailored hydration strategy can help you run smarter, safer and stronger.

References

• Armstrong, L.E. (2021) ‘Rehydration during endurance exercise: Challenges, research, options, methods’, Nutrients, 13(3), p. 887. doi:10.3390/nu13030887.

• Cheuvront, S.N. and Kenefick, R.W. (2014) ‘Dehydration: physiology, assessment, and performance effects’, Comprehensive Physiology, 4(1), pp. 257–285. doi:10.1002/cphy.c130017.

• Cheuvront, S.N., Carter, R. and Sawka, M.N. (2007) ‘Fluid balance and endurance exercise performance’, Current Sports Medicine Reports, 6(4), pp. 202–208. doi:10.1249/JSR.0b013e3180a02ca8.

• Hew-Butler, T. et al. (2015) ‘Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference’, Clinical Journal of Sport Medicine, 25(4), pp. 303–320. doi:10.1097/JSM.0000000000000221.

• Maughan, R.J. and Shirreffs, S.M. (2008) ‘Development of individual hydration strategies for athletes’, International Journal of Sport Nutrition and Exercise Metabolism, 18(5), pp. 457–472. doi:10.1123/ijsnem.18.5.457.

• Noakes, T.D. (2007) ‘Drinking guidelines for exercise: What evidence is there that athletes should drink “as much as tolerable”, “to replace all the weight lost during exercise” or “ad libitum”?’, Journal of Sports Sciences, 25(7), pp. 781–796. doi:10.1080/02640410600875036.

• Sawka, M.N. et al. (2007) ‘American College of Sports Medicine position stand. Exercise and fluid replacement’, Medicine & Science in Sports & Exercise, 39(2), pp. 377–390. doi:10.1249/mss.0b013e31802ca597.

• Shirreffs, S.M. and Sawka, M.N. (2011) ‘Fluid and electrolyte needs for training, competition, and recovery’, Journal of Sports Sciences, 29(S1), pp. S39–S46. doi:10.1080/02640414.2011.614269.

• Shirreffs, S.M. and Maughan, R.J. (1998) ‘Volume repletion after exercise-induced volume depletion in humans: replacement of water and sodium losses’, American Journal of Physiology, 274(5), pp. F868–F875. doi:10.1152/ajprenal.1998.274.5.F868.