Place chicken in a large zip-top plastic freezer bag. Add buttermilk and hot sauce; seal and refrigerate at least 2 hours or overnight.
Remove chicken from buttermilk mixture; lay flat on baking sheet.
Heat oil to 350 degrees F.
Combine salt, garlic powder and pepper. Sprinkle chicken with seasonings: set aside.
In a large but shallow dish (such as a 13 x 9-inch pan) combine cornstarch, flour, baking powder and water; mixing well to make a batter.
Dip chicken into batter a few pieces at a time, being careful to allow excess batter to drip off.
Using tongs, slowly place chicken into hot oil.
Cook in small batches, turning frequently 15-20 minutes or until evenly browned and done. Chicken should reach 165-170 degrees F.; use a meat thermometer for accuracy.
Drain on wire rack over paper towels.