Simple Syrup: In a medium saucepan bring the sugar and water to a simmer. Simmer for 5 minutes until the sugar crystals are dissolved. Cool completely.
Pour the syrup into a half gallon pitcher then add the pineapple juice, apple juice and lemon juice. Mix to combine.
Chill thoroughly for at least 4 hours or overnight.
Just before serving add the chilled seltzer water, stir well.