Pour the sugar and 1/2 cup of water into a small saucepan and bring to a boil over medium high heat for 5 minutes stirring frequently. Remove from heat and set aside to cool.
Puree the watermelon in your blender. If there were seeds, strain the mixture through a fine sieve.
Pour the sugar mixture into a large pitcher. Add the remaining water, lemon juice, watermelon juice and ice. Stir until well combined and chilled.
You can add some sliced or cubed watermelon and lemon slices to your pitcher for added flavor and to make it look pretty for a garden party or picnic.
This can be made well ahead of time and stored in the fridge. Or make a batch of lemonade and add the watermelon puree before serving.