In a saucepan, combine the water and granulated sugar. Heat over medium heat, stirring frequently, until the sugar completely dissolves, creating a simple syrup. Remove from heat and let it cool.
In the 1-gallon dispenser with a spigot, combine the lime juice and the cooled simple syrup. Stir well.
Add the mint leaves to the dispenser and muddle them gently using a muddler or the back of a wooden spoon.
Pour in the white rum and give it a good stir to combine the ingredients.
Add the club soda to the dispenser and stir gently.
Fill the dispenser with ice cubes, leaving some room at the top for garnish and easy pouring.
Place lime slices and mint sprigs on top of the ice for garnish.
Close the dispenser securely and let it sit in the refrigerator for about 30 minutes to allow the flavors to meld together.
To serve, open the spigot and pour the mojito into individual glasses. Garnish each glass with a lime slice and a mint sprig. Sit back, relax, and enjoy the tropical goodness!