Put cranberries, sugar, and water in a saucepan over medium-high heat and bring to a boil.
Once boiling, lower heat to medium low and let cook for another 10 minutes, until berries start bursting.
Strain the juice into a heat-proof bowl, leaving the solids behind, and place bowl in fridge to cool.
In a glass filled with ice, pour half the vodka, half the pomegranate juice, and half the lemon juice. Repeat with second glass. Pour 1 ½ oz. cranberry simple syrup in each glass and top glasses off with soda water.
Garnish with cranberries and pomegranate arils, if desired