This is lovely and moreish, if a bit of a faf.
Squeeze some lemons.
For every 4 floz of lemon juice, put 5 floz of water, 6 tablespoons of sugar and 1 teaspoon of grated lemon rind in a saucepan and bring to the boil, stirring continuously. Boil for 5 minutes, stirring regularly.
Allow to cool then add the lemon juice.
Bottle and chill.
Dilute 1 part lemonade to 3 or 4 parts sparkling water, depending on your taste.