Gather the watermelon chunks, sugar, and lime juice on the countertop.
4 cups fresh watermelon chunks
Add the sugar and lime juice to the blender, then pour in the watermelon chunks. Blend until smooth and uniform, about 30 seconds, with a slightly frothy top.
4 cups fresh watermelon chunks, 1/4 cup granulated sugar, 2 tablespoons lime juice
Pour the blended mixture into a shallow dish or baking tray, spreading it out evenly.
Place the dish in the freezer. Every 30 minutes, use a fork or spatula to scrape and stir the mixture, breaking up ice crystals into coarse, flaky shards. Repeat this process 3-4 times until the entire mixture is icy and granular.
Once the granita has reached a fluffy, crystalline texture, serve it immediately in glasses or bowls. Garnish with a small lime wedge if desired.