Lightly oil a large baking sheet. In a medium saucepan, bring the sugar, corn syrup and water to a boil, stirring just until the sugar dissolves. Stop stirring and cook over moderately high heat until the syrup turns an amber caramel, about 5 minutes. Stir in the butter and nuts. Add the baking soda and stir just until foamy. Immediately pour the caramel onto the prepared baking sheet. Let cool, then crack into 1/2-inch bits.