Put 100 ml of water together with the sugar in a saucepan and bring it to a boil. Let the water simmer gently while stirring until the sugar is dissolved. Let the sugar water cool before continuing.

Squeeze the lemons and add the juice to a carafe or bottle.

Add the rest of the water and sugar water and stir well.

Put it in the refrigerator to cool completely, and serve the lemonade with ice cubes and lemon slices if desired.