Watercolor pencils look the same as 'normal' pencils, but if you check the lettering stamped on them you'll see a little symbol to show they're water soluble, such as a water droplet or a small brush, or the word 'watercolor'. Of course, you can always just do a quick test on a scrap bit of paper to test.
Using a water-soluble pencil or crayon where you didn't intend to can result in disaster if you use paint over the drawing or sketch, smudging it. So if you mix your types of pencils up, always check!
