Hydration · lesson 3 of 9
Electrolytes — water needs a wingman
Sodium, potassium, magnesium and chloride are what let water do its job.
5 min read · reviewed October 2026
Drinking plain water isn't the whole story. Water follows electrolytes — charged minerals that set the osmotic gradients controlling where fluid goes. Drink a lot of plain water while low on sodium and you can actually dilute your blood, which is both ineffective and, in extremes, dangerous.
The four electrolytes that matter most
The main driver of fluid balance in the blood and between cells. You lose it in sweat — which is why heavy sweating needs salt, not just water. It also powers nerve signaling.
The dominant electrolyte INSIDE cells; it balances sodium. Higher potassium intake (from fruit, vegetables, legumes) supports healthy blood pressure. Most people get too little.
A cofactor for hundreds of enzymes (300+ by the classic estimate), including the sodium-potassium pumps that maintain the gradients. Commonly under-consumed; low magnesium is linked to more cramping and poorer sleep.
Sodium's partner anion; together they're most of your extracellular charge. It also makes stomach acid. Usually covered automatically when sodium and diet are adequate.
You did a long, sweaty workout in the heat. What's the smartest rehydration move?
- Drink as much plain water as you can, fast
- Replace fluid AND sodium (and ideally potassium)
- Only worry about it if you cramp
- Sip a sugary soda — the sugar is what matters
Show the answer →
B.Replace fluid AND sodium (and ideally potassium)
Sweat contains a lot of sodium. Replacing only water dilutes your remaining electrolytes and can leave you feeling worse. Add sodium (and some potassium) — that's the entire point of electrolyte/sports drinks for hard or hot sessions.