In a medium bowl, mix together flour and salt. In a separate bowl, mix together egg, milk, water and melted butter. Add wet mixture to dry mixture and mix until combined. (Your batter will be much thinner than typical pancake batter.) Set the batter aside to rest for 15 minutes.
When you are ready to cook your crepes, heat an 8” skillet over medium-high heat. Coat the bottom of the skillet with a little butter. Pour enough batter into the hot skillet to just barely coat the skillet, turning the pan so that the batter covers the entire bottom.
Cook the crepes for 1-2 minutes on the first side. (If the skillet has been properly greased, a firm shake will release the crepe from the skillet when it is ready to flip.)
Flip the crepe when the top is starting to look dry, and cook for an additional 10-15 seconds on the second side.
Remove the crepe from the pan and wrap in a tea towel to keep soft and warm. Re-grease the skillet if needed and repeat with the remaining batter.
To serve, place a layer of filling down the middle of the crepe and fold the sides over the filling.