Halve the lemons, cut a slice from half. Squeeze the lemons. Put the lemon juice in a glass and add the cane sugar. If you prefer something sweeter, add a teaspoon of sugar. Top up with mineral water, add a few leaves of peppermint and put in a straw. Stir well and decorate the edge of the glass with the lemon wedge. Chill in the refrigerator for half an hour.