You can use Woodland Scenics Water Tint which is specially formulated to tint Deep Pour Water, Realistic Water and Surface Water. Or you can use Earth Colors Liquid Pigment to tint Realistic Water. Pour Realistic Water into a disposable cup and mix in coloring agent very slowly to avoid bubbles. If bubbles occur, cover and let set until they disperse (approximately 2 hours). It is advisable to do a small test area to verify desired color. Instructions are available on the Woodland Scenics website.