Make the simple syrup by adding the granulated sugar and water together in a small saucepan. Heat on medium high just until the sugar dissolves. Set aside to cool down.
Juice your lemons, discarding the seeds. Stir in the passion fruit.
Add the water and the simple syrup. Stir in as much of the water and simple syrup as desired to reach your preferred level of sweetness and tartness.
Chill until ready to serve. The passion fruit seeds will sink, so give it a good stir before serving.