Add 4 TBSP watermelon and 4 TBSP cucumber to 4 cups of kombucha. Store in bottles for 1-3 days in a warm, dark place. Toss the remaining watermelon and cucumber pieces on your counter into a blender and blend until smooth. Strain the liquid through a fine mesh sieve. Discard pulp and store the juice in your fridge for later use in the coolers. 

In 1-3 days when the second fermentation of your kombucha is complete, strain out the fruit from the kombucha and combine in a pitcher with the chilled watermelon / cucumber juice. Stir in some ice along with the lime juice and tequila (if using). Fill 8 glasses with ice and divide the kombucha cooler evenly among them. Garnish with mint sprigs, serve, and enjoy!