Jim,
A lot of folks like to use play sand instead of water in the water pan, for a long smoke like a brisket, to avoid refilling the water pan.
Another option, is to purchase a Brinkman charcoal pan, to replace the Weber water pan for a long smoke. It even fits more securely on the brackets, than the Weber pan. The Brinkman charcoal pan holds twice the amount of water as the Weber water pan, and costs about $5.00.
Good luck on your first smoke.