To a medium saucepan, add the elderflower, sugar and water. Set over medium heat and stir until sugar dissolves. Bring the mixture to a simmer and then immediately turn off the heat, cover the pan and allow to steep for 1 hour. Pour the syrup through a strainer and into a pitcher and discard the elderflowers.

To the strained syrup, add the freshly squeezed lemon juice and top with the water. Refridgerate until chilled, at least 2 hours. To serve, add a few ice cubes and then garnish with elderflower.