Put the water and butter in a pan and bring to the boil. Remove from the heat and add the flour and a pinch of salt, then beat until the paste is smooth and forms a ball. Allow to cool slightly. Gently beat the eggs then gradually add them to the pan, beating all the while, to form a smooth, shiny paste.
Spoon this mix into a piping bag fitted with a 1" (2.5cm) plain nozzle and pipe small mounds of the mixture onto greased baking sheets. Bake in a preheated moderately hot oven (Mk 6 - 400ºF - 200ºC) for 15-20 minutes until risen and golden.
Transfer to a wire cooling rack, allow to cool, then split each one and fill with the double cream (heavy cream), lightly whipped.
Gently melt the chocolate and water in a pan (if it's too thick, add a little more water). Arrange the profiteroles on a dish and spoon over the chocolate (or, alternatively, dip the profiteroles into the melted chocolate). Place the remaining chocolate in a sauce boat so people can help themselves. Serve immediately.