Cut the rind off a small seedless watermelon and cut into 1-inch cubes. Place the cubes in a large bowl and freeze for at least 4-5 hours, or up to overnight, until solid.

Transfer the frozen watermelon cubes, lime juice, and ice to a high-speed blender. Blend on high, using a tamper to push down the chunks, until the mixture is smooth and almost creamy, about 1-2 minutes.

If the slushie is too thick, add a tablespoon of water at a time and blend until desired consistency is reached.

Pour the refreshing watermelon slushie into chilled glasses or bowls and serve immediately with a spoon or straw. Garnish with a lime wedge if desired.