I have some artists pastels that are water soluble, it depends on the binder and the brand. I vaguely remember some of my pastel pencils are as well. You can draw with the pastel stick, then blend with a wet brush or spray with a water bottle, but its not something I have experimented with much.
I've used colour pencils and acrylic paints with pastels frequently with good results, acrylic always under pastels, colour pencils over blended pastel, but I have found this only works on sanded paper like Art Spectrum Colourfix.