Cut melons into half. With a spoon, scrape seeds and pulp. Place pulp and seeds in bowl, add 1 cup of the water and repeatedly press down with the back of spoon to extract flavor. In a fine mesh sieve, strain. Discard seeds and reserve the juice.
Using a melon shredder, shred cantaloupe meat. In a pitcher, combine shredded cantaloupe, the reserved juice (from straining pulp) and the remaining 3 cups water.
Add condensed milk and stir to disperse. Serve in glasses over ice. Consume immediately.
I used one full can of condensed milk to allow for the dilution of the mixture from ice. If serving it without ice, adjust amount of condensed milk according to desired sweetness.