Combine spinach, flour, sparkling water, eggs, Parmesan cheese, baking powder, garlic, vinegar, salt, and black pepper together in a bowl until batter is evenly combined.
Heat enough oil to cover the bottom of a large skillet over medium heat. Spoon batter into the hot oil, keeping about 1 inch between each croquette. Cook until golden brown, about 90 seconds per side. Repeat with remaining batter.
