(modified from Highballs High Heels)
Pour lime juice, lemon juice, and ginger syrup into a 10-oz. glass and stir. Add a splash of raspberry syrup and top off with the seltzer. Add ice cubes if desired. Garnish with 2 or 3 whole raspberries. A sprig of mint could also be nice.
Bring water to a boil in small saucepan. Lower the heat and stir in the sliced ginger. Cover and remove pan from heat. Let stand for 1 hour or until desired flavor intensity has been reached.
Strain out the ginger pieces, and bring the ginger water to a boil again over medium-high heat. Remove the pan from the heat and slowly add the sugar, stirring all the while, until the sugar is completely dissolved.
Let cool completely. Pour syrup into a clean glass jar and cap tightly. Store in the refrigerator and use as needed. Syrup will keep in the refrigerator for up to 2 weeks.