I built by second UDS earlier this year. At first I was all about the water pans, but did not like the texture it gave the meat. I was going thru TOO MUCH water, and it was making the meat super moist and mushy.
When meat fibers cook, they turn to gelatin- too much moisture gives you meat flavored gelatin. Not appetizing at all.
Now, I use a 1/8" thick steel diffuser plate with a couple large holes cut out, mounted 5" from the top of the coal basket. It keeps the heat more even from the top of the cooking area to the bottom, catches most of the drippings while still allowing some to fall thru to the coals, and keeps the flare-ups to a minimum.
If you're seriously concerned about retaining moisture in the meat- foil it 2/3 way thru the cook. It will do the same thing only better, plus it will do what a water pan can't- collect some of the juices for later use.
That's my humble .02
"Eating 'Que isn't making me fat- it's the beer I drink while lounging by the pit."