1 (4-pound) cantaloupe, seeded and cut into 1-inch cubes (about 8 cups)
1 1/2 cups water
1 tablespoon fresh lime juice
1 tablespoon sugar
1 quart chilled club soda or seltzer
Garnish: lime wedges; honeydew melon slices
Purée cantaloupe in batches with water in a blender. Transfer to a colander lined with a kitchen towel (not terry cloth) or fine cheesecloth set over a deep bowl and let drain 1 hour. Gather ends of towel and very gently squeeze any remaining juice from melon, then discard solids.
Stir in lime juice, sugar, and 1/4 tsp salt and chill 1 hour.
Divide among 8 (10-ounces) glasses and top off with club soda