Place the lavender in a serving jug/pitcher; pour the boiling water over the lavender; cover with plastic wrap and allow to steep 10 minutes; pass through a sieve and discard the lavender from the water. Return the water to the serving jug/pitcher. Add the cold water, lemon juice and sugar to the serving jug/pitcher and stir until the sugar dissolves. Refrigerate until serving.
If unavailable, substitute in dried lavender buds to taste.