In a mixing bowl, whisk together flour and eggs. Gradually add in milk and water, stirring to combine. Add salt and melted butter; beat until smooth.
Heat a lightly oiled non-stick skillet over medium-high heat. Pour or scoop the batter onto the skillet, using approximately ¼ cup for each crepe. Tilt the pan with a circular motion so that the batter coats the surface evenly.
Cook the crepe for about 2 minutes, until the bottom is light brown. Loosen with a spatula, turn and cook the other side. Keep warm while preparing the filling.
In a separate pan, melt butter over medium heat. Add apples, brown sugar, and cinnamon. Cook until apples are tender and caramelized, about 5-7 minutes.
Spoon apple mixture into the center of each crepe and fold over. Serve warm.