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Marathon fueling

How Much Water to Drink During a Marathon

Drink to thirst with sodium in the plan. Forced plain-water gallons raise hyponatremia risk; racing bone-dry raises heat and GI risk. No universal ounces-per-mile.

Sports dietitian review pending

How much water to drink during a marathon is a range problem, not a slogan. Sweat rates commonly span about 0.3–2.4 L/h in ACSM-style summaries (Sawka et al., 2007). Forcing the same cup count on every runner creates two failures: dehydration in heavy sweaters and exercise-associated hyponatremia (EAH) in people who overdrink dilute fluid (Hew-Butler et al., 2015).

This page is in-race fluid. Starting euhydrated is vegan race-morning hydration. Sodium sources are electrolytes for marathon runners. Heat edits the frequency of sips in running a marathon in the heat.

Educational only — not treatment for hyponatremia or heat stroke.

The rule that survives 2026 consensus

Drink to thirst once you are moving, with sodium in the plan, after starting the day already euhydrated. Do not chase a body-weight percentage invented on race morning. Do not drink a cup at every table because the volunteer is holding it out.

Hew-Butler et al. (2015) emphasize that EAH is largely a function of fluid intake exceeding losses — often plain water or very dilute drinks over many hours. Slower marathoners are over-represented because they have more time and more tables.

Key takeaway: There is no universal ounces-per-mile. Start hydrated, sip to thirst, put sodium in at least one practised fluid, and treat “drink at every station” as a habit to unlearn if you finish bloated with a headache.

What “enough” looks like (without fake precision)

| Signal | More likely meaning | Adjustment to practise | | --- | --- | --- | | Thirst, dark urine pre-gun | Started behind | Use the morning protocol; do not “catch up” with a gallon on course | | Dry mouth, salt crust, fading in heat | High losses | More frequent sips of a practised sodium-containing drink | | Tight rings, sloshing stomach, clear urine, headache | Overdrinking dilute fluid | Skip cups; get sodium from a practised source; do not add more water | | Gel-paste nausea | Concentration + low fluid | Water with the packet; lower g/h if needed | | Confusion, vomiting, collapse | Medical | Stop self-coaching |

ACSM 2007 discusses limiting body-mass loss from dehydration while avoiding overdrinking. Individual numbers move with weather, body size, and pace. This site will not publish “16 oz every mile” as a rule.

Carbohydrate still has to land. A 4-hour marathon at 60 g/h is 240 g of carbohydrate. That math does not disappear because you are managing cups. Build both columns in the vegan race fuel planner.

Water vs sports drink vs sodium-only

| Fluid | Catalog example (Aug 2026) | Job | | --- | --- | --- | | Plain water | Course cups | Fluid only — pair with gels that need it; do not exclusive-gallon this in heat | | Carb + sodium drink | Tailwind Endurance Fuel 25 g / 310 mg; Neversecond C30 drink 30 g / 380 mg; Skratch Sport 21 g / 380 mg | Fuel + fluid + sodium | | Carb-forward, modest sodium | Maurten Drink Mix 160 40 g / 160 mg | Fuel in the bottle; plan extra sodium if you are a salty sweater | | Sodium-only | LMNT 0 g / 1000 mg; PH 1500 0 g / 1500 mg | Salt vehicle — still need carbohydrate |

All named products above are manufacturer-confirmed vegan on this catalog, not Certified Vegan. Tailwind Rebuild and Skratch Recovery are dairy. Course “electrolyte” cups are unknown SKUs until you read them in training or on the athlete guide.

Most gels still want water. Maurten Gel 100 is 25 g in a small volume; SiS GO Isotonic Gel is 22 g / 10 mg sodium and is marketed as needing less extra fluid — still practise that claim. Concentrated carbs plus a shut gut is a documented GI pattern (de Oliveira et al., 2014; Costa et al., 2017).

A training method instead of a slogan

  1. Weigh yourself (same state of undress) before and after one long run in similar weather. The change is a crude sweat-rate clue, not a race-day prescription. Account for fluid drunk and urine if you want a tighter estimate — or skip the scale and use thirst plus how you finish.
  2. Practise the exact bottle concentration you will race.
  3. Rehearse aid-station choreography: walk or slow, drink, discard, restart fueling cadence.
  4. If you are a back-of-pack finisher, decide in advance which tables you will skip.
  5. If you have a history of EAH, collapse, or kidney disease, stop crowdsourcing fluid rules and see a clinician.

Race week still uses 8–12 g/kg carbohydrate and the ~15 g fiber/day heuristic so you are not fighting residue on top of fluid (carb-loading guide). Glycogen already stores water; aggressive extra drinking on top of a completed load is usually unnecessary.

Frequently asked questions

How much water should I drink during a marathon?
There is no universal ounces-per-mile. ACSM fluid-replacement guidance aims to limit excessive dehydration without forcing large volumes of low-sodium fluid. Practical method: start euhydrated, drink to thirst at aid stations you have practised, and put sodium in at least one fluid source. Sweat rates vary from well under 0.5 L/h to over 2 L/h.
Can you drink too much water in a marathon?
Yes. Exercise-associated hyponatremia is more often tied to overdrinking dilute fluid than to “not enough salt tablets.” Slower runners who drink at every table out of habit are over-represented in consensus statements. Symptoms can include bloating, headache, nausea, confusion, and in severe cases seizures.
Should I drink at every aid station?
Only if that matches thirst and a practised plan. Grabbing every cup is a habit, not a protocol. Know whether the cup is water or a branded mix, and whether that mix is a vegan SKU you have used.
How is this different from race-morning hydration?
Race morning is about starting euhydrated (for example 400–600 ml in the two hours before the gun, adjusted to thirst). This page is in-race fluid once you are moving. Do not stack a gallon of plain water on a completed carb load.
Do gels replace water?
No. Most concentrated gels need water. Maurten Gel 100 is 25 g carbohydrate in a small volume. Taking packet after packet with no fluid is a common nausea pattern, especially in heat.
What should I drink if I am a salty sweater?
Practise a carbohydrate drink in the ~300–600 mg sodium per litre class, or a sodium-forward packet plus gels, on warm long runs. Do not invent a milligram prescription from a white shirt stain.

Sources

  1. Sawka, M. N., et al. (2007). American College of Sports Medicine position stand: exercise and fluid replacement.
  2. Hew-Butler, T., et al. (2015). Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference.
  3. Thomas, D. T., Erdman, K. A., & Burke, L. M. (2016). ACSM Joint Position Statement: Nutrition and Athletic Performance.
  4. de Oliveira, E. P., Burini, R. C., & Jeukendrup, A. (2014). Gastrointestinal complaints during exercise.
  5. Costa, R. J. S., et al. (2017). Systematic review: exercise-induced gastrointestinal syndrome.

Educational content only. Carbohydrate, fiber, iron, B12, and hydration needs vary. Consult a sports dietitian or physician for individualized guidance — especially if you have a GI condition, anemia, or a history of underfueling.