Bring the sugar with 100 ml of water to a boil.
Boil for approximately 1 minute.
Remove from the heat and allow to cool.
Finely chop the watermelon.
Puree with a mixer.
Combine the syrup, lemon juice and rosewater.
Add to the watermelon puree.
Place the mixture in a flat metal container.
Freeze for at least 4 hours, stirring well with a fork every half hour for the first 3 hours.
Fill small bowls with the granita and serve.