They help maintain fluid balance. But how does it actually work in practice?
Electrolytes are minerals that become electrically charged when dissolved in water. The most important ones for the body are sodium, potassium, magnesium, calcium, and chloride. Once they are dissolved in the body’s fluids, they allow water to move and help send signals throughout the body.
Osmosis – how the body moves water
The basic mechanism behind fluid balance is osmosis. Osmosis means that water moves through cell membranes from areas with a low concentration of dissolved substances to areas with a higher concentration. If there’s more sodium on one side of a membrane, water will automatically move in that direction to restore balance. In this way, the body controls where water goes—into the bloodstream, between the cells, and inside the cells.
How water moves through the body
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Intestines: When you drink, water and electrolytes first end up in your intestines. Here, special transport proteins are activated—including SGLT (Sodium-Glucose Linked Transporter). These require both sodium and a bit of glucose to efficiently move water and sodium from the intestines into the blood.
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Bloodstream: Once water is absorbed from the gut, it is transported around the body in the blood. Here, electrolytes help ensure the right distribution of fluid, so the blood isn’t too thick or too thin.
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Around the cells (extracellular): Water moves out into the tissues and between the cells, regulated by the balance between sodium and chloride.
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Inside the cells (intracellular): Potassium plays a special role in moving water into the cells, where it’s used for energy production and other processes.
SGLT – why glucose matters
SGLT proteins in the gut work best when both sodium and some glucose are present. This enables the body to absorb fluids and electrolytes faster than if you only drink plain water or a highly concentrated salt solution. That’s why hypotonic electrolyte drinks often work better than plain water or very salty/sugary mixtures.
How do we lose electrolytes?
The body loses electrolytes in several ways:
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Sweat: Mainly sodium and chloride, but also some potassium and magnesium.
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Urine: The kidneys excrete excess electrolytes—especially sodium and potassium. This one is particularly important when drinking alcohol.
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Diarrhea and vomiting: Here, you can lose large amounts of sodium, potassium, and chloride in a short time.
Why is the balance important?
If you lose too many electrolytes—or only replace lost fluids with plain water—the body can’t keep water where it’s needed. This can lead to symptoms like muscle cramps, fatigue, headache, or in the worst case, serious disruptions to body functions. That’s why both water and electrolytes are necessary, especially during hard exercise, hot weather, or illness with fluid loss.