Put sugar and water in a medium saucepan, along with blood orange zest and juice, over medium heat. Bring to a boil. Lower heat to a simmer and let mixture simmer for about 10 minutes.
Pour simple syrup into a heat-proof bowl or mason jar and pop it in the fridge to cool.
Once blood orange simple syrup is cooled, spoon about 2 ounces into each glass.
Add about a cup of ice cream into each glass and fill to the brim with soda water.
Serve ice cream sodas with straws and blood orange granishes.