First, gently snip the elderflower blossoms away from the thicker green stems — keep as much of the delicate flower as possible.
Make a simple syrup by dissolving the sugar in 1 litre of boiling water. Leave to cool. Pour this into a clean 5-litre bucket or large fermentation jar.
Top up with the remaining 3.4 litres of cold water, then stir in the lemon juice, lemon peel, vinegar, and elderflowers.
Cover loosely and leave at room temperature for 48 hours. Give it a gentle stir once a day to keep everything happy and submerged.