How to make
Wash the lemons very carefully, squeeze out their juice and put it away in the fridge. Blend the rinds in a blender or meat grinder, pour 4 1/5 cups (1 L) of water over them and put in the fridge for 24 hours.
The next day, drain out the water, pour in the lemon juice and the sugar. Stir until the sugar dissolves, then add the citric acid as well.
Keep the resulting mixture in the fridge. Before consumption, dilute with water or sparkling water to taste.