Watermelon-Lime Soda

Combine sugar, water, and ginger in a small saucepan over high heat. Cook until the sugar is dissolved, stirring with a whisk. Remove from heat; cover and let stand for 15 minutes. Strain; remove dry matter. Combine the diced watermelon and fresh lime juice in a blender; whisk until smooth. Strain the watermelon mixture through a fine sieve into a jug; discard the dry ingredients. Add sugar syrup and chilled soda. Serve with ice; garnish as desired.