The lever could either unleash horrible death or open access to some new area. Or both.
Really, there's not much need to make a decision with this information, unless there's some serious time pressure. Further exploration may reveal some barred areas which the lever may open. Checking for traps is another low cost way to hedge your bet.
Many monsters could use a source of fresh water in their lair. PC type foes in the dungeon would indicate that the banquet wouldn't be totally out of line. Sometimes the damsel in distress really is a damsel. It's not like you can't take a few precautions to minimize the danger in each case. And a modicum of professionalism means characters aren't likely to swimming around for fun, pigging out, or dating while on a quest or treasure extraction anyway.
If everything in the dungeon is bad, then why even go there? The treasure could be cursed items and those coin crawler monsters after all. Is an attitude of clinical paranoia really fun, and does cultivating such an attitude on the part of the GM make for a better game?