Symbolism, Imagery, Allegory
The Ganges is a big deal to the Mehtas. In fact, it's the reason they have Hari marry Koly in the first place. They desperately need the money to bankroll a trip to the river, so they take Koly and her dowry before Koly's family gets hip to the fact that their son is dying. So what's the deal with the river anyway?
The Mehtas—and many other Hindu people—believe that the Ganges has real magical powers. According to Chandra, you don't even have to see the river itself to benefit from it. She tells Koly before the trip, "'I have only to touch you and I will share in your darshan, your sight of the holy Ganges. That is all I ask'" (3.2). That's one mighty river, right? Right.
Even though the Mehtas the river can cure all kinds of nasty ailments, though, it doesn't work for Hari. So perhaps the Mehtas are duped by the river in much the same way that they trick Koly's parents into agreeing to let their daughter marry Hari. Instead of saving Hari's life, the trip to the Ganges only ends it, leaving his parents devastates and Koly a widow.