To prepare rhubarb syrup: In a small saucepan, add sugar, water, and rhubarb and bring to a boil. Boil until the sugar has dissolved and the mixture has reduced slightly.
Strain the syrup into a glass container (with lid) and let it cool uncovered in the fridge for at least 1 hour.
In a large pitcher, stir the club soda, rose water, and a 1/2 cup of the rhubarb syrup until combined. Add more syrup if desired.