What would happen if someone allergic to water is stuck in a desert and finds a bottle of distilled water to drink and they drink it?

I read some news articles on people who have a severe allergy to H2O molecules that if they drink water their throat can close up and blister and they cannot touch water either. They have to rely on liquids that aren't water to survive.

So let's say one of them is stuck in a desert and they run out of their normal non water drinks and they're dying of dehydration but find a bottle of distilled (pure) water to drink, and then they drink it all in one go. What would happen?