Start by preparing the watermelon. Cut the watermelon into cubes and remove any seeds if necessary.
In a blender, combine the watermelon cubes, freshly squeezed lime juice, honey or agave syrup (if using), and ice cubes.
Blend on high until the mixture is smooth and slushy. You may need to stop the blender and stir the mixture with a spatula to ensure everything blends evenly.
Taste the slushie and adjust sweetness with more honey or agave syrup if desired. Blend again if you add any sweetener.
Once blended to your desired slushy texture, pour the watermelon slushie into serving glasses.
Garnish with lime wedges, if desired, and serve immediately for the best flavor and texture.
For a more intense lime flavor, add a bit of lime zest to the slushie before blending.
If you prefer a colder drink, you can freeze the watermelon cubes for a couple of hours before blending.
This slushie is a great base for adding other fruits like strawberries or mango for additional flavors.