Cover the strawberries and basil with the sugar. Refrigerate for 24 hours, then add the red wine vinegar.
Let sit for another 24 hours, then stir to dissolve any remaining sugar and strain out the solids.
Serve in a Collins glass over ice and top with sparkling water, to taste. (Strained solids can be reserved and made into jellies or sauces—they also have wonderful flavor.)