I use a water brush when I use watercolor pencils, but I do not fill the barrel. I just dip the tip in the water. I have arthritis in my hands and the waterbrush is so much more comfortable for me to hold. I have the old chunky aqua colored ones. I just dip the tip in the water and wipe it off. It takes Very Little water and it goes a long way. I am always amazed.
When doing it this way, I never get the big drops of water to ruin my project.