In a blender, combine the diced pineapple and coconut water. Blend until smooth. Strain the mixture through a fine mesh sieve into a large pitcher, discarding the pulp.
Add the fresh lime juice, mint leaves, and simple syrup to the pitcher. Use a muddler or the back of a spoon to gently press the mint leaves to release their flavor.
Stir in the white rum until well combined.
Fill glasses with ice cubes and pour the mojito mixture over the ice, filling each glass about two-thirds full.
Top each glass with club soda to your desired fizziness. Stir gently to combine.
Garnish with additional mint leaves and a slice of lime, if desired. Serve immediately.