Boil water in a pot with sugar and let it cool down again.
Slice the lemon and add together with the citric acid.
Wash lavender flowers and lavender leaves well, drain and mix in as well. Cover well with plastic wrap and let steep for at least 3 days.
Then strain and pour into a hot rinsed, well-sealed bottle (or canning jar).
Keep the lavender syrup in a cool place.