Grease a large baking sheet generously with butter and place it in a warm oven at 250º F. (You can also use Silpat liner and grease it).This will make spreading the hot mixture easier later. In a nonstick saucepan combine the water, corn syrup, and sugar over medium heat. Place the candy thermometer in the saucepan. Cook while stirring gently using a silicone spatula. Keep stirring until all the sugar is melted and the thermometer reads 240º F. This will take more than 5 mins.