Place the 7 cups of cubed watermelon into a blender and blend until smooth. Strain the watermelon juice using a fine-mesh strainer to remove any seeds or pulp, reserving the juice.
Add fresh watermelon juice, lime juice, triple sec and white wine to large pitcher. Stir to incorporate.
If your wine is fully chilled, you can serve immediately. If not, chill for 1 to 2 hours before enjoying this cocktail.
Right before serving, gently stir the watermelon and wine mixture together again. To serve, pour 2 parts of watermelon sangria over ice and top with 1 part chilled seltzer water.
Garnish with fresh blueberries and watermelon stars if desired.
Notes
White Wine: Use a dry white wine like Pinot Grigio, Sauvignon Blanc, Chardonnay, or Dry Riesling.Triple Sec: Grand Marnier, Brandy, and Cointreau are all delicious, albeit pricier substitutes for the triple sec, and will add a rich undertone to this sangria as well as delicate notes of citrus. Seltzer: Adding plain seltzer water adds a nice effervescence to this Sangria, but feel to omit it. Storage: This Watermelon Sangria will keep for 3 days in the refrigerator.