Combine water and chopped mint in a small saucepan.

Bring the mixture to a simmer for 2-3 minutes to infuse the mint flavor.

Add sugar to the mint-infused water and stir until dissolved.

Remove the saucepan from heat.

Stir in the lime juice.

Allow the syrup to cool completely.

In a blender, combine cubed seedless watermelon and ice.

Blend until smooth.

Strain the mint syrup to remove the mint leaves.

Add the strained mint syrup and white rum to the blended watermelon.

Adjust the amount of rum to taste.

Pour the watermelon mojito into cocktail glasses.

Garnish with mint sprigs or watermelon slices, if desired.

Serve immediately and enjoy!