Prepare your simple syrup by bringing 2 cups of fresh (and clean) lilac flowers, 2 cups of sugar, and 4 cups of water to a boil in a saucepan.
Lower to medium heat, stirring constantly, and cook until the sugar has dissolved. Leave to cool.
While your simple syrup is cooling, juice lemons and strain the seeds (see below for store-bought conversion).
Once cool, strain the flowers from your syrup and add 1 cup of the simple syrup to a pitcher (save the rest in an airtight jar for later).
Slowly combine lemon juice and simple syrup in a pitcher. Mix well!
Add remaining water and mix well. For best results, chill for a minimum of one hour before serving.
Adjust the lemon juice and simple syrup to taste and serve over ice with a sprig of fresh lilac flowers for garnish.