The Complete Hydration Guide
Daily habits, electrolyte balance, and adjusting for heat and activity level.
Daily baseline
Fluid needs vary by body size, climate and activity level, so there is no single number that fits everyone -- a practical check is urine color: pale yellow generally indicates reasonable hydration, dark yellow suggests you need more fluid.
Electrolytes, not just water
Sodium, potassium and magnesium are lost through sweat alongside water. For long or hot sessions, replacing electrolytes alongside fluid helps the body actually retain what you drink, rather than just passing it through.
Adjusting for conditions
Heat, humidity and altitude all increase fluid and electrolyte needs -- training in hot conditions or at altitude is a reasonable time to add an electrolyte drink even for a session you would not normally need one for.
Worth knowing
Significantly over-drinking water without replacing electrolytes can also cause problems in rare cases (hyponatremia) during very long endurance efforts -- balance matters more than volume alone.
