In a large saucepan add the water, sugar, elderflowers and the lemon.
Bring to the boil and simmer for 5 minutes.
Leave all the ingredients to cool completely and then strain out the liquid.
Add the cold liquid to an ice-cream machine and churn until set or alternatively pour in to a container and freeze stirring every 30 minutes until made. The mix should be soft enough to scoop and hold its shape.