In a medium pot, placed over medium low heat, combine the water and sugar. Heat until the sugar dissolves, about 2 minutes. Take the pot off the heat and place the fresh mint sprigs in the water mixture; cover the pot and allow it to steep for at least an hour to two hours. Pour the mixture into a large casserole dish and cover with plastic wrap; freeze for 2 hours. At the 2-hour mark, remove it from the freezer and using a fork, scrap the ice until it resembles a slushy and return to the freezer. Freeze for at least 4 hours, ideally overnight.