Hydration and electrolytes: no universal litre target

Start with daily hydration, then training

The NHS suggests most people aim to drink enough during the day for clear pale-yellow urine; long physical activity or hot conditions may increase fluid needs. That is a daily observation, not a precise race-day formula. Running needs also depend on intensity, sweat rate, clothing, altitude and acclimatisation.

Do not drink to a fixed litre target

“One litre per hour” may be too much or too little depending on the person and conditions. Track weight change around long runs, thirst, urine colour and stomach comfort to find your range. Do not drink large volumes to “prevent” dehydration in one session; excessive fluid can also create a low-sodium risk, especially in long events.

More electrolytes is not always better

Sweat loses water and salt, but sweat volume and sodium concentration vary widely. Normal food and drink are usually enough for short runs; electrolyte drinks may help in long, hot or high-sweat situations, but trial them in training. Do not use salt tablets or concentrated drinks as a substitute for recognising heat symptoms.

Heat exhaustion and heat stroke

The U.S. National Weather Service lists heavy sweating, weakness, dizziness, nausea, headache and fainting among heat-exhaustion signs. Heat stroke can include confusion, slurred speech, very high body temperature, a rapid strong pulse or loss of consciousness; it is an emergency. Call local emergency services and cool the person while waiting. Do not treat heat stroke by telling the runner to drink more and continue.

What this page does not provide

This page does not prescribe individual fluid volumes, salt doses or electrolyte formulas, and does not diagnose dehydration or low blood sodium. People with kidney or heart conditions, or those taking diuretics or other medication, should discuss fluid plans with a clinician. Seek medical help for persistent vomiting, altered consciousness or marked swelling.

Sources and scope

Daily fluid and urine-colour guidance follows the NHS hydration page; heat-illness recognition follows the U.S. National Weather Service. Both are general information, not individual medical advice.