Put marshmallows in a microwave safe bowl and sprinkle the water over them. Microwave in 30 second intervals, mixing with a spatula between, until marshmallows melt and become smooth (the mixture should not be hot enough to burn you). Dump melted mixture out onto a surface greased well with Crisco (it will spread out), use the spatula to scrape it off the sides of the bowl. Pour most of the powdered sugar over the mixture (it will spread out even more). Grease your hands thoroughly with Crisco and start to knead the sugar into the mixture. Knead until smooth (maybe 5 minutes). If you want to color the fondant, now is the time to do so. I used regular water-based food coloring and it worked fine. Knead the coloring in (the Crisco on your hands should keep the coloring from dying you) until there are no color streaks (maybe 2 or 3 minutes). Pat the fondant into a ball and coat lightly with Crisco. Wrap tightly in plastic wrap and refrigerate for at least 3 hours (overnight is fine). When you are ready to work with the fondant, zap it in the microwave for 10 to 20 seconds to soften it up. It's now ready to be rolled out, cut, and shaped. If you're covering a cake, the cake should be frosted first using a buttercream frosting so that the fondant has something to stick to. Don't roll the fondant too thin, 1/6 of an inch seems about right.