Place the sugar and about 3 cups of the water into a large pot and heat, stirring regularly, just until sugar dissolves. Remove from heat and add the remaining water and orange juice.
Add the whey, stirring to mix.
Use a funnel to pour into individual flip top bottles or bottle with screw top lids.
Allow to sit in a warm area for a few days, checking occasionally for flavor. We keep our home pretty cool overnight, so I found that placing a small desktop lamp near the bottles overnight sped up the fermentation process.
As soon as the sodas are fermented to your liking, transfer them to the fridge until ready to drink.