The sand and water are nothing more than heat sinks to help control temps. The sand is preferred by some, including me until lately, due to it's stability in controlling temps and the ease of clean-up. You just, fold the grease in the foil and throw it away, then refoil again.
In my WSM, I used a Brinkmann charcoal pan, filled it little over 1/2 with play sand, smooothed it out then foiled over the sand, to catch the drippings.
I might add one thing, when using sand it is imperative to control temps on their way up, if they get too high it's hard to bring them down. But if you start controlling them when your pit reaches around 200-210, it'll settle right in for you around 225.
Treasurer, Great Lakes BBQAssociation
Rubbed, Smoked, and Sauced Competition BBQ Team-
22 1/2" WSM, 2 18 1/2" WSM's, 22 1/2" Weber Kettle