Heat water in a saucepan over medium heat. Add sugar one cup at a time, stirring after each addition until the sugar dissolved. Mixture will become thick. Remove from heat.
Stir in food coloring now, if desired. Let cool for 10 minutes.
Meanwhile prepare wooden swizzle sticks or string. Run through water and then coat thickly in sugar. Let dry completely.
Pour sugar mixture into 6 (8-oz.) jars. Using clothespins (or a pencil for string) to suspend swizzle sticks 1 inch from the bottom of the jar. Be careful for the sticks/string to avoid the edges of the jar. Cover with saran wrap and set in a cool, dry place.
Allow rock candy to rest and form for 2 weeks. Once it has grown to around 1-inch diameter, remove from the sugar syrup and let dry on a plate. Discard remaining sugar syrup and crystals.
Notes
Please make sure to supervise and help children as the rock candy syrup is very hot and dangerous.