1 cup filtered water
3 tablespoons sugar (more/less to taste)
5 cups chopped seedless watermelon (about 1 1/2 pounds)
3 cups filtered water
3 tablespoons fresh lime juice, or to taste
3 to 4 fresh mint leaves for garnishing
Combine 1 cup water and sugar in a saucepan; bring to a simmer over medium-high heat, stirring until sugar is dissolved. Add hibiscus flowers; remove from heat, cover and let steep for 10 minutes, then strain, discarding solids. Set aside to cool.
In a blender, puree watermelon with 2 cups filtered water until smooth. Strain through a fine mesh sieve to remove solids.
Pour into a glass along with remaining 1 cup water and hibiscus sugar mixture; stir in lime juice to taste. Chill until ready to serve with mint leaves on top of the drink.