In a medium mixing bowl, whisk to combine the all-purpose flour, cornmeal, granulated sugar, baking soda and salt.
In another bowl, whisk the buttermilk, water, eggs and melted butter until smooth and well-blended.
Pour the wet mixture over the dry ingredients slowly. Gently fold them in, just to combine, being careful not to over-mix, in order to preserve the light, airy quality of the cakes.
Lightly butter a large skillet or griddle and place it over medium heat. Grease lightly with a little butter or non-stick spray.
Using a ¼ cup measure, ladle batter into the hot skillet, cooking 3 to 4 cakes at a time, depending on the size of your pan.
Cook the cakes for 4 to 5 minutes, or until the edges set and bubbles start to form on the surface. Carefully flip the cakes and continue cooking for 2 to 3 more minutes, until both sides are golden brown.
Serve the Johnny Cakes warm, with maple syrup and a sliver of butter, if you like.