In a blender, add the cherries, lemon juice, and sugar. Blend until smooth and then run the cherry syrup through a mesh strainer. You can store this syrup in the fridge until ready to use.
Fill a glass halfway with ice. To the glass, add 3 tablespoons of cherry syrup. Top with sparkling or still water and stir. Garnish with lemon slices and fresh cherries. [Note: If you are making this with still water, you can make a whole pitcher and store it in the fridge. If you are using sparkling water, its best to make it by glass so that the sparkling water does not go flat.]