There's just not enough writing (writing that has found itself before my eyes, anyway) about the hazards of getting wet. Dungeons are dank, dripping places often enough, but hardly ever has the wetness itself be a problem in my games. Say, just two weekends ago my Bahamuddan cleric was wading free as duck in waist-high frogwater, to say nothing of the juices of the frogs' interiors but not even his fussy white boots were any worse for wear.
So, with no more effort than it takes to type it (which is really the only kind of effort you'll find on this blog), here are the effects of falling in foul pools that should be making PC's cheap lives miserable:
Wet armor padding. It's at least going to slow you down. Maybe make it harder to swing your great-grandsire's single-edged sword, The Gummer. Maybe it's ruined altogether. If you want to keep that harness on, it's gonna chafe.
Wet thief's boots. You're probably gonna squeak, Sneaky.
Wet bowstrings. Yes, I wish you had written down "oilcloth to wrap extra bowstrings" too. Sodden arrows and fletchings probably don't work so well either.
Wet Spellbooks. This has huge potential. I can't believe I've never read the phrase "wet spellbook" before. Scrolls are going to be vulnerable to the smears as well.
Fssssss! Your torch went out. Aww, and the rest of 'em are soaked through as well. You didn't happen to make note of how your flint and steel were stored, did you? Too bad you weren't playing 4e and you could use one of those kewl glow-wands. Barf.
Soggy food. Uh, sure you can still eat it. What's your Constitution score? Thanks. Oh, and do you know what page the disease rules are on?
Foot blisters. Walking around all day in slippery boots and mushy skin has got to be hard on even the most iron-thewed. Maybe my milquetoast modern daintiness is showing through here--but shouldn't road worn feet be a concern to adventures even on the driest delves?
I'd love to hear about how you handle water hazards and suggestions for where to find treatments of these things in actual rules.