Place the cantaloupes on a flat surface and split them in half. Scoop out and discard the seeds. Use a spoon to scoop out the flesh in small increments. The goal is to tightly pack 3 cups of cantaloupe flesh.
Place the cantaloupe in the blender and add the lemon juice and cider. Puree until smooth and taste for seasoning. Add the sugar, if needed. Use the water if more liquid is needed. Pour the soup into a medium bowl. Make an ice bath to chill the soup by combining some ice cubes and cold water in the bottom of a larger bowl. Put the soup in the ice bath and store in the refrigerator until ready to serve.
Season the cucumber lightly with salt and pepper. When ready to serve, pour the soup into the chilled bowls and add some of the cucumber to each.