I quit using water after being too slow to clean out the smoker after a couple late cooks and coming back a couple days later to find mold inside that required a thorough cleaning. I also had a few long cooks when all of the water in the pan evaporated before the meat was done causing a major temp spike and I had to try to add more water without disrupting the food or the fire. That was a pretty major hassle.
I eventually switched to play sand and couldn't be happier with the results. If it takes longer to heat up (personally, I haven't noticed this) it's because the sand is a better thermal mass than water and the sand will be more effective at stabilizing temps during the cook. It also can't evaporate, so you don't have to worry about temp spikes when your water baffle disappears. Finally, I haven't seen so much as a speck of mold since switching to sand. I'm sold and will never go back.
When I do whole turkeys I typically leave the pan out to achieve higher temps in the smoker, and it works great that way too.