Start by preparing the syrup. In a medium saucepan, combine the white sugar, water, and lemon juice. Set the pan over medium heat and stir the mixture until the sugar completely dissolves. This should take approximately 5 minutes. Once the sugar has dissolved, remove the saucepan from the heat and allow the syrup to cool in the refrigerator for about 30 minutes.

Meanwhile, take the cubed watermelon and process it in a blender or food processor until it is smoothly pureed. Integrate the chilled syrup into the pureed watermelon, ensuring a homogeneous mixture.

For the final step, pour the watermelon mixture into an ice cream maker. Freeze it according to the manufacturer's instructions until it reaches your desired consistency. Enjoy this refreshingly light sorbet as a delightful treat to beat the heat!