Puree cantaloupe or watermelon in a food processor and pour through a fine sieve to eliminate pulp. In a pitcher, mix strained fruit puree with water and add sugar, lime juice, and salt, to taste.
This and other similar fruit drinks, which translate literally as "fresh water," are served all over Mexico and they're a cinch to replicate at home. The key is to strain the pulpy fruit to make a clearer liquid. Instead of melon, you could use strawberries, pineapple, mango, or any fruit that is soft enough to puree.