Preheat the oven to 200 C / Gas 6. Line a baking tray with baking parchment.
In a saucepan, bring the water, sugar and butter to the boil. Reduce the heat, and add the flour and salt all at once. Beat with a wooden spoon until the paste is smooth and begins to pull away from the sides of the pan. Remove from the heat.
Beat in the eggs, one at a time, mixing well with each addition. The paste should be smooth and sticky. Using a tablespoon, drop 2 to 3cm balls onto the prepared baking tray. Sprinkle each ball with granulated sugar, pressing it lightly into the surface.
Bake in the preheated oven until puffed and golden, about 20 minutes. Cool on a wire rack.