Mr. Picasso's art room I didn't have as many markers to put in the water so the colors weren't too bright the first day. They worked even better the next day. Or two of my sons used the markers themselves after they had soaked a bit and got some vibrant colors that way too. I think just soaking the markers for a few minutes or putting a drop of vinegar on the tip as another pin suggested would revive a lot of dry markers.
My kids are really loving drawing and painting. I'm loving how simple it is to make them happy and creative. :)