Cut the lavender flowers from the stems (no need to strip) and place in a medium bowl (a large pyrex measuring bowl works great because you can pour easily from it).
Pour the sugar over the flowers and use your (clean) fingers to gently rub the flowers into the sugar.
Pour 2 cups of boiling water over the lavender sugar and stir with a spoon until the sugar has melted.
Cover and let infuse for 30 minutes (or up to several hours).
Strain the lavender-infused simple syrup and pour into a serving carafe or pitcher.
Stir in the lemon juice.
Add another two cups of water. Add more lemon juice if too sweet. Add more sugar if too strong.
Add ice and more water to desired level of concentration.
Serve with a sprig of lavender, or add some purple food colouring to make it even Instagram-friendly!