The brush is actually like a brush marker tip with no reservoir of ink. The tube is hollow with no way to add water. (If there were a way to add water, this might actually be a cool tool.) You dip the brush tip into the little cups of fluid which are really cups with foam in them. The fluid doesn't spill because the foam keeps it all soaked up. (I suspect it is washable marker ink as it is NOT watercolor paint.) When you're done, you pull the white pad out of the blue tray and wash it and the brush in the sink and it totally washes out. No fuss. No mess.
The packaging gives instructions to wash everything out and not to let it dry on the pad or brush. The regular pigmented paints did not wash out of the tip but stained it. The packaging also says not to get it on the wallpaper, painted walls, vinyl flooring, etc. My guess is that once dry or with the right combination of materials you'll have a problem on your hands. I found no real value in the brush, which was what I was after in the first place. It was like using a dried out marker to watercolor with. Not much blend-ability with either their paint or my own. Verdict: Don't waste your time or money unless you're 6 years old.
You may have to enlarge the image, but you can see where the "brush" started to make the paper in the Moley roll up and peel. Not pretty. I'm not particularly hard on my other brushes or my paper nor are there a lot of layers on this. Just a bad combination.