Combine sugar, water, and ginger in large saucepan. Bring to a boil over medium heat and stir until sugar dissolves. Once sugar dissolves, remove from the heat and let stand until cool. Strain through a fine sieve.
In a large pitcher, combine the cooled ginger syrup with the soda water and bourbon. Stir to combine. Fill 16 tall glasses with ice and top with the ginger-bourbon mixture. Garnish the rim of each glass with an orange slice and serve immediately.
Note: For individual serving, combine 2 tablespoons of syrup with 1/4 cup of bourbon and a little over 1/2 cup of soda water.