Jalapeño-Watermelon Margaritas

Puree watermelon in a blender until smooth. Strain through a fine-mesh sieve and transfer the liquid to a large pitcher or measuring cup (discard the pulp). Stir in tequila, Triple Sec, lime juice and agave (or simple syrup). Fill 6 glasses with ice and the margarita mixture. Add a few jalapeño slices to each drink and serve with lime wedges.