Include electrolytes when hydration demands are high

Water alone is not always sufficient — sodium is the primary electrolyte lost in sweat, and replacing it aids fluid retention and prevents dilutional imbalance.

Why it works

Sodium is the primary osmotic driver of plasma volume; drinking large amounts of plain water without sodium replacement dilutes plasma sodium (hyponatremia), which paradoxically worsens hydration status by blunting thirst and increasing renal excretion. For ordinary daily conditions, dietary sodium (from food) is usually sufficient. In heat, prolonged exercise, or high-sweat conditions, an electrolyte source prevents the dilutional effects that pure water can cause at high intakes.

How to do it

1. For ordinary daily hydration, food-sourced sodium is sufficient — no special electrolyte drinks needed.
2. During or after heavy exercise, heat exposure, or illness with fluid loss, a moderate electrolyte source (sports drink, salted food, electrolyte tablet) alongside water is appropriate.
3. Avoid routine electrolyte supplements as a daily habit without high sweat conditions; unnecessary sodium is not beneficial.

Evidence

The role of sodium in fluid retention and plasma volume regulation is well-established in physiology; exercise-induced hyponatremia from excessive plain water intake is documented and clinically recognized. (mechanistic)

Electrolyte imbalances from ordinary daily hydration in healthy people without extreme conditions are uncommon; the primary risk group is endurance athletes and those with very high sweat rates. Do not over-generalize the electrolyte need to ordinary daily drinking.

Sources

• Noakes et al. (2005), three independent biological mechanisms cause exercise-associated hyponatremia, British J. Sports Medicine

Common mistake

Adding commercial electrolyte drinks to an already-adequate hydration routine in the belief they improve everyday performance — most contain added sugars and calories that provide no benefit when sweat losses are normal.