In a small saucepan put 1/2 cup water and 1 cup of sugar. Stir and simmer until the sugar is dissolved. Cool.
In a large drink jug put in 4 oz fresh lemon juice, 2 oz fresh passion fruit juice (no seeds) and 3 ½ cups of water and the cooled syrup. Chill.
For a passionfruit mojito, add rum, muddle with fresh mint and add ice.