This is a simple bug, related to the changes that alert you if you will be unable to finish something when you try and consume it. Drinking from a RV kitchen, and then replying to the prompt about being too full to finish the drink causes you to instead take a unit of water and put it in your inventory.
Probably something with how it gives you water and you immediately drink it. Just don’t let the option show when slacked.
Maybe it’s a feature, like in Dwarf Fortress, you can store liquids in your inventory lol