- In a saucepan, bring the water and sugar to a boil, stirring until the sugar has dissolved. Let cool.
- In a flat 8-cup (2 litre) airtight container, combine the watermelon juice and lime juice. Add the syrup and mix thoroughly.
- Cover and freeze for 6 hours or until completely frozen.
- Using a fork, scrape the granita into icy crystals. Serve immediately in chilled bowls.