Cut the watermelon into cubes, removing any seeds if present, and measure 4 cups of the flesh.
Bring 2 cups of water to a simmer in a kettle or saucepan. Remove from heat and add dried jasmine flowers. Cover and steep for 5 minutes to infuse the water with jasmine aroma.
Strain the jasmine-infused water through a fine mesh strainer into a measuring jug, discarding the flowers. Allow the infusion to cool slightly.
Place the watermelon cubes into the blender with 1 cup of the warm jasmine-infused water. Blend until completely smooth and vibrant pink.
Pour the blended mixture through the fine mesh strainer into a pitcher to remove any pulp for a smooth consistency. Stir in honey or sweetener if desired and chill in the refrigerator for at least 10 minutes before serving.
Serve the watermelon jasmine juice in glasses, optionally garnished with fresh mint or a small wedge of watermelon, and enjoy the refreshing aroma and flavor.