Preheat oven to 450 degrees F (230 degrees C). Line a baking sheet with aluminum foil.
Mix salt and flour together in a bowl; mix water in gradually until a thick paste forms.
Spread 1/3 of the salt mixture onto prepared baking sheet to form 1/2-inch thick bottom crust. Place snapper onto bottom crust; cover fully with remaining salt mixture to form 1/2-inch thick top crust.
Bake in the preheated oven until crust is golden brown, 25 to 30 minutes.
Crack crust with a fork; remove crust and skin from snapper to serve.