Isn't that pretty much the opposite of what I'm thinking of? If you walk in the desert you get dehydrated, and won't urinate as much. I don't seem to be able to explain what I mean very well. I found my dictionary, but the word wasn't included, so I'll try once more to explain:
I'm looking for a word that describes a medicin (or other substance) that increases your amount of urine.
Edit: I've found it! (Through googling and comparing Swedish medical texts to English ones.) The word I was looking for is Diuretic
. I probably shouldn't use the word unexplained in the game, though. I doubt many non-native speakers are familiar with it.