To make the cucumber juice , puree 2 peeled seedless cucumbers in a blender with a touch of water. Pour the puree through a fine mesh strainer into a large measuring cup.
In a large pitcher, combine the cucumber juice, lime juice, vodka and simply syrup. Stir well then refrigerate for at least 1 hour. Before serving, pour in the cold seltzer water, starting with 1 cup. Taste and if desired, add in more simple syrup and seltzer. Pour the mixture over crushed ice and garnish with lime wedges and cucumber slices!
Also, if you really want to UP the cucumber flavor, you can use cucumber vodka.