Yea see I don't even know what you're talking about with the water/foil balls because I have never seen a WSM in person so I'm not sure what parts are in it. I've seen pics of sand in a bowl though.
Oh, I see. Sorry.
The WSM has a bowl/pan where the user can place water, other liquids, or things like sand, clay plates, foil balls (I'm sure there are others) to act as a heat diffuser and shield from direct heat. The bowl goes under the grates, but above the fire ring...hanging on it's own supports. [Trust me, when you see it, you'll get it...the WSM is so easy to assemble that even I could do it]
I have found that using water makes it more difficult to get the WSM hot quickly and then as the water boiled out, temps changed. I don't know if others had that problem, but I did. As soon as I started using foil, no problems.
For the foil, I filled the bowl about 75%-80% full with balls of foil about the size of my fist. Then I wrap the top of the bowl with a layer of foil. Some use several top layers, so they can just tear one off after the cook. I really like this system so far.
Also, the WSM retains heat very well. On one of my first cooks with mine, we used it to cook treats for the cooks at a benefit BBQ. We took the food off and shut down the vents. I forget what time of day that was, BUT after several hours, I went to load up the WSM and it was too hot to handle. The thing is great for fuel use and heat/moisture retention.
I love mine...sure you'll love yours, too. If not, I'll give ya $50 for that piece of junk
LOL