My serpentine belt has been replaced a couple of times, but in wet weather it comes off while driving. My only thought is the water pump pulley. Is it supposed to have a groove on it that keeps the belt on? My thought is it is worn and causes it to "walk off" but I'm stumped.

It seems like you have a shield missing of some sort and when it is wet, the water pump pulley or tensioner pulleys are getting wet, and the belt is sliding off.

Hmm, i find it strange, my shield is off too, (wheels turned, you can see the crank pulley and oil filter.) But the belt stays on.

Pull the belt off, and check the condition of the belt. No cracks? Frayed edges, etc?

Check the tensioner and all pulleys. No looseness, all move with ease? If you can't find anything wrong with the above, try running a waterhose on each pulley till you find one that slips off. BtW, make sure all pulleys are perfectly in line, and nothing appears out of line.

Most belts stay on simply because of the other pullies in the path with grooves to hold the belt. If your belt is slipping, the tensioner is a suspect, as are any worn pulleys that might be allowing the belt to walk and slip off.

Where are you located?

Had a similar problem. Mine started squealing a lot so I threw some belt dressing on it, helped for about 5 minutes. I got home and put more on and the belt just walked right off, it did seem a bit loose. I went to autozone and got a new one, put it on, I had to crank the tensioner way the crap back in order to get the new one on, and its not coming off.

I suspected maybe my tensioner was bad, thus giving a loose belt but that wasnt the case for me. You said yours has been replaced a couple times so I can't say get a new belt, but check to make sure the tensioner is actually keeping it tight.