Some people(including me now) put an 18" clay saucer wrapped in foil inside the water pan. It heats up to the temp of the smoker and helps regulate the temp and also seems to extend cooking times. The experts are split on the water vs. no water. Jamie Purviance, who writes many Weber cookbooks, says use water. Harry Soo who is a top 10 bbq competition cook does not use water. It works either way. I haven't been able to tell a difference in ribs, chicken or butts. I have not tried a brisket without the water in the pan yet. Brisket may be the one meat I may stick with the water. Clean up is a little easier without the water though. Try it both ways and see what you think. The 22 WSM is a great smoker. A tip I'll share - if you use water spray the inside of water pan with Pam grilling spray and don't foil. It cleans up fine by rinsing out with a water hose.
18 WSM; 22 WSM; 26.75 OTG; Blue Weber Performer