Why is this dangerous?
When a pet takes in water faster than the kidneys can excrete it, blood sodium is diluted. Water then moves into brain cells, which swell inside the fixed skull — the cause of the neurological signs.
The classic case is a dog repeatedly fetching from a lake or playing in a sprinkler for a long time, or a dog that drinks an enormous bowl after intense exercise. Small dogs are at higher risk.
Why speed matters
Delaying care significantly worsens outcomes. Some signs appear hours or days later, so "looks fine right now" is not a reason to wait.
Signs to watch for
- Lethargy, confusion, staring into space
- Wobbliness, staggering, unable to stand
- Dilated pupils, blindness-like behaviour
- Drooling, vomiting, excessive urination
- Tremors, seizures, coma and breathing difficulty in severe cases
What to do right now
- Call the vet immediately — hyponatraemia needs careful, slow correction; too-rapid correction causes its own brain injury.
- Stop the pet drinking and remove it from the water.
- Do not give salt, salty food or electrolytes on your own.
- Limit water play: take breaks, use a shallow pool, and do not let a hot dog gulp a full bowl at once.
If your pet shows any of the signs above, go to the nearest emergency vet now and call ahead.
The step-by-step response, from the first minute to the vet visit, is in our Water Intoxication (Hyponatraemia) emergency guide.