SIADH · Syndrome of Inappropriate ADH

A broken water-saver with a stuck faucet

Imagine your home's water tank has a smart float sensor that turns off the inlet faucet when the tank is full, keeping pressure steady. In SIADH, that float sensor is broken or stuck, so the faucet never closes — water keeps trickling in even though the tank is already overflowing. The tank (your blood) gets more and more water added to the same amount of salt (like dissolving one salt shaker into a bigger bucket), so the saltiness of the water drops dangerously. Meanwhile, the overflow drain (your kidneys' ability to dump dilute urine) is blocked because the broken faucet mechanism is also forcing the drain valve shut, trapping water inside. Your body tries to bail itself out by pumping some salt out through a side door (ANP telling kidneys to waste sodium), but it is not enough — the tank keeps swelling with dilute water. If you suddenly crank open the drain all the way (correcting sodium too fast), the pressure drops so fast that the pipes freeze and crack (osmotic demyelination of brain nerves).