Pour half of the water into a saucepan, and bring to a boil over medium heat. Add the garlic and garlic powder, and boil until the water has almost evaporated, about 5 minutes. Stir in the heavy cream, parsley, salt, and pepper. Mix the cornstarch with the remaining water, and stir into the sauce. Cook, stirring constantly, until thickened, about 3 minutes.
