LogFAQs > #932196356

Thirst is related to hydration, but they're not completely linked. You can quench thirst to a certain extent by just swishing water around in your mouth without actually swallowing any, and getting IV fluids will sate dehydration without immediately quenching thirst. The body extrapolates feelings of hydration based on the presence of water in the mouth: the loss of blood pressure and increase in blood solute concentration associated with dehydration doesn't go away until several minutes after you drink water, but the mere feeling of swallowing water signals the brain to stop telling you you're thirsty so you'll stop drinking.

The extension of this is that anything that moistens or dries out your throat to a degree that doesn't align with how well it will hydrate will quench/worsen your thirst without having the same effect on your actual hydration levels. It'll balance out in the long run as your body processes the drink and adjusts your perception of thirst based on where your hydration levels stand, but in terms of immediate thirst, "most hydrating" and "most thirst-quenching" aren't necessarily the same thing.