1 1/3 cups fresh watermelon juice (see Cook's Note)
One 12-ounce bottle ginger beer
3/4 cup vodka
1/4 cup freshly squeezed lime juice (2 limes)
Sprigs of mint and lime wedges, for serving
Fill 4 tumblers with ice.
If you can't find fresh watermelon juice, you can make your own by pureeing chunks of fresh seedless watermelon and pouring the puree through a mesh strainer before measuring the juice in a glass measuring cup.