Cut the ginger into slices about 2 to 3 coins thick. Add to a saucepan along with the honey and water. Bring to a light boil, stirring occasionally. Then lower the heat to a simmer and let cook for 5 minutes. Turn off heat and let steep for 30 minutes. Strain out the ginger, then let cool completely in the fridge.
Combine ginger syrup, grapefruit juice, vodka, and orange liqueur in a pitcher. Stir to combine, then pour in the sparkling water.
Serve over ice, garnished with fresh grapefruit slices. Top with extra sparkling water if desired, and enjoy!