Boil 2 cups of water in a saucepan.
Remove from heat and add dried lavender. Steep for 15 minutes.
Strain the lavender infusion into a pitcher.
Combine the remaining 2 cups of water and sugar in the saucepan.
Heat gently until sugar dissolves.
Add the lemon juice to the pitcher with the lavender infusion.
Pour in the sugar-water mixture and stir well.
Refrigerate for at least 30 minutes.
Serve over ice, garnished with lemon slices and fresh lavender.