Squeeze the lemons into a bowl so as to collect all the juice, then grated the fresh ginger and add it to the lemon juice.
Strain the lemon juice and the grated ginger, pressing the pulp into the strainer with the back of a spoon to extract the essence of ginger.
Pour the lemon juice in a jug or a bottle, add the sugar and stir until dissolved, then water it down with cold water. The amount of water will depend on how intense you like it: I usually use 1/3 of lemon juice and sugar and 2/3 of water.
Serve the ginger lemonade with ice cubes and a few sprigs of fresh mint.