Instead of checking for resistance, you might take a spring clothespin apart, and drill out the jaws to mount a couple of small brass bolts on each jaw. Wrap your wires around the bolt, and tighten down with a nut. Re-assembled the clothespin; when the jaws are closed, the "switch" is closed and current can run through the wires (wire one side to ground, the other to a digital pin, set the internal pull-up and monitor).
Put an uncoated aspirin tablet between the jaws (so the contacts don't close), and set it on the floor, with the edge the aspirin touching the floor. When the floor gets wet, the aspirin will soak it up, fall apart, and the jaws close, making contact.
This kind of "sensor" was described in one of the many "Engineer's Mini-Notebooks" written by Forrest M. Mims, III (http://www.forrestmims.org/
), but I believe it predates that publication by likely decades (I'm sure I saw something like it in an old Popular Science magazine from the 1940s or earlier).