No, not a crack, a smart and resourceful comment. That's exactly what they needed. Humans can survive for weeks w/o food, but only about 3 days w/o water. In those hot/humid conditions on a black rooftop with no shelter, perhaps less than 3 days. They needed rain. Hopefully a few less people will die if they collect some rainwater.
The rule of the three's. Under extreme conditions your survival, given decent physical condition, is generally:
3 hours for enviro (think wet and naked w/extreme temps)
3 days hydration (maximum)
3 weeks nutrition.
Intoduce illness, disease, or injury, and each of these markedly decrease survivability; without human intervention.