Place the powdered sugar in a medium bowl. If it contains lumps, sift it first for a smoother mixture.
Stir together the corn syrup, vanilla extract, and start with 1 tablespoon of water in the bowl until a smooth icing begins to form. Add additional water if desired consistency has not been met.
Continue mixing until the consistency is thick enough to hold its shape but soft enough to pipe. If needed, add a few drops of water or a little extra powdered sugar to adjust the texture.
Divide the icing evenly among small bowls.
Tint each portion with a different food coloring and stir until the colors are evenly distributed.
Transfer each color to its own piping bag or zip-top bag. Cut a very small opening in the tip.
Line a baking sheet or tray with parchment paper. Pipe long, thin strands of icing across the parchment.
Leave the piped icing uncovered at room temperature until completely firm and dry. Depending on humidity, this can take anywhere from 12 to 24 hours.
Once hardened, use a knife to cut the strands into small sprinkle-sized pieces.
Let the cut sprinkles sit for another hour if needed to ensure all sides are fully dry before storing.