I used water for the first 4-5 smokes when I got my WSM. A big problem for me living in a subdivision is what do I do with all of the grease water? I can't put it down the drain because the grease will clog your main drain over time. I can't toss it in my .20 acre yard because it will attract pest, rodents (skunks love Weber grease), stray pets and possibly larger critters like fox and coyote. I tried mixing it with white vinegar and baking soda then dump it in a newspaper lined trash bag.
That is when I converted to a foil covered 16" clay saucer and wrapping the entire water pan in foil. When done, unwrap and throw everything in the trash. The foil on the clay saucer usually lasts 2-3 smokes depending on how well I wrap the water pan.
I can't tell the difference in meat flavor, moistness or maintaining temp because both water and the clay saucer serve as a heat sink just one is more constant and does not evaporate. The big difference for me is during the cleanup. I'm a weekend smoker. If I start prep and smoking Friday evening, I am usually "done, done" early Sunday afternoon ie everything put away, all meat portioned and sealed, everything cleaned and stored.
My 2 cents