Bring 1 cup water to a boil in a medium saucepan. Combine the boiling water and lavender in a medium bowl; cover and steep 30 minutes. Strain the lavender mixture through a fine sieve into a bowl; discard lavender leaves.
Combine 3 cups water and sugar in saucepan. Bring the mixture to a boil, and cook 1 minute or until sugar is dissolved. Combine lavender water, sugar syrup, and lemon juice in a pitcher. Cover and chill. Serve over ice. Garnish lemonade with lavender stems, if desired.