In a small saucepan, heat water, sugar, and pitted cherries until the sugar has completely melted. Using a potato masher, smash the cherries. Strain through a fine mesh strainer and cool over an ice bath. Once the cherry simple syrup has reached room temperature, fill a shaker with ice. Add the vodka, lemon juice, and 1 ounce of the simple syrup. Shake to combine and strain into a rocks glass over ice. Top with club soda and garnish with fresh cherries.