I have used water and sand in my Excel 20, but I switched to using a 14 inch clay saucer (like you would put under a flower pot). I foil the water pan and the saucer and put the saucer in the water pan. My view is that water, sand and saucer all act as a heat sink and make it easier to control the temperature. I switched to the saucer because it is lighter than the sand. Plus, drippings always seemed to get into the sand, even with foil over it, so you either have to keep replacing the sand or it becomes very yucky.
I haven't noticed any difference in the moisture of the meat using sand or saucer instead of water.