My WSM has a large water pan and I think that it really serves two functions. First and probably most important is that it helps regulate the heat inside the smoker. Second is that it keeps the inside of the cooker moist. I've read some conflicting articles about the moisture. Some say that you get a better smoky taste without the extra moisture. I know a few people who put sand instead of water in the pan. Still helps to regulate the heat but without the moisture. I use water in the pan and I've always had very good results.