Wash the ingredients.
For the cucumber, 2 options: either in slices, or you grate it in a cloth placed in a bowl then you press by rolling the cloth and you recover the water of cucumber.
Place them in a large pitcher.
Then pour 1,5 liters of water into the pitcher and add lemon slices and mint leaves.
Let it sit in the refrigerator for a few hours, overnight if possible, and enjoy it with a few extra ice cubes.