Put the flour and salt in the bowl of a standing mixer (or in a large bowl if you are whisking this by hand). With the mixer running, pour in the milk, water, melted butter, orange zest and eggs. Whisk until the batter is smooth.
Heat a 7-inch frying pan or crêpe pan until it is very hot. Using a paper towel, wipe the surface of the pan with a little oil. Pour just enough batter to coat the bottom of the pan, just under 1⁄3 of a cup. Tilt the pan to coat evenly. Cook the crêpe until the bottom is golden brown and then flip it over, cooking a minute more. (You may lose the first one or two as they might stick or not form properly. Don’t worry; this is normal.)
Keep the cooked crêpes in a stack on a warm plate.
When ready to serve, place a crêpe on a plate, drizzle with orange juice and a little sugar. Fold in half and half again. Serve warm.