Blend the pineapple with 2 cups of water until smooth.
Pour the puree into a clean container.
Add sugar, remaining water, and optional ginger. Stir well.
Sprinkle yeast on top and cover loosely (allowing air to escape).
Let ferment at room temperature for 2–3 days, tasting daily until desired fizziness and sweetness is achieved.
Strain the liquid into bottles and chill before serving.
Serve cold as a refreshing, slightly fizzy drink.