Chill 4 martini glasses.
In a blender, add water, cantaloupe, sugar, and lime. Puree in blender until liquid consistency. Strain into a measuring cup. Fill a martini shaker with ice cubes. Pour in 1 part melon vodka to 2 parts cantaloupe juice. Shake vigorously.
To serve, pour into chilled martini glasses. Garnish with a slice of lime or drizzle lemon liqueur over the top and let sink to the bottom.