As a high school art teacher I am always snooping around for new art supplies and techniques. A few months ago I stumbled onto a watercolor brush that has a water depository in the handle. I bought a couple of different brands in different price ranges when I had a chance and I am TOTALLY in love.
I was concerned that the brush fibers might mildew if left damp for very long, that it might leak and I was also concerned about the quality of the brush tip (whether it would hold it's shape or be too soft or hard). Not a one of these problems has happened and I've used the heck outta the Sakura Koi brush. I love the ease of using this brush for the lettering on my dictionary drawing series.
I think these brushes would be ideal for watercolorist who likes to travel but hates hauling around water containers. I have to admit that I don't switch around my color palette that often but when I needed to, the brush washes easily in water. To dampen the brush you just lightly squeeze the barrel of the brush handle.
Here's a resource if you are interested: