Whisk water and eggs together in a small bowl. Mix bread crumbs and garlic salt together in a medium bowl. Blend flour and cornstarch together in a third bowl.
Heat oil to 365 degrees F (185 degrees C) in a large, heavy saucepan.
Dredge a mozzarella stick in flour; shake off excess. Dip into egg mixture. Lift up so excess egg drips back in the bowl. Press into bread crumbs to coat. Place breaded mozzarella stick on a plate or wire rack. Repeat with remaining mozzarella sticks.
Use a spider spoon or a pair of tongs to lower 3 to 4 mozzarella sticks into the hot oil. Fry until golden brown, about 30 seconds. Remove from heat and drain on paper towels. Repeat to fry remaining mozzarella sticks.