1.Remove the rind thinly from one of the lemons and cut into thin strips (or use a zester). Combine the lemon rind, sugar, citric acid and tartaric acid in a large heatproof bowl.
2.Pour boiling water over sugar mixture, stir until sugar is dissolved. Squeeze the juice from the lemons; you will need 1 1/4 cups (310ml) juice. Stir the juice into the sugar mixture; cool.
3.Strain the lemon mixture into sterilised bottles and keep refrigerated.
4.To serve, use two pails (round-shaped, handled container or bucket) of lemon syrup to one part soda water (or iced water), or mix to taste.
Alternatively to ready-to-drink lemonade, this recipe makes 2.5 litres of syrup. Undiluted lemon mixture will keep up to two weeks in the fridge.Note