Electrolyte balance is the state of the body’s dissolved salts — sodium, potassium, chloride, calcium, magnesium, phosphate — held within the narrow ranges that cells need. These charged minerals govern fluid distribution, nerve impulses, muscle contraction, and blood pH; too high or too low, and the consequences run from cramps and confusion to cardiac arrest. The kidneys are the master regulators, adjusting excretion to intake, while diet supplies the raw materials: sodium from salt, potassium from fruit and vegetables, calcium from dairy. Illness disturbs the balance — vomiting and diarrhoea waste potassium and water, kidney failure retains them — which is why oral rehydration salts are formulated to precise electrolyte ratios. Sports drinks trade on the same science. Electrolyte balance is the chemistry of staying alive, measured in millimoles.