At about 21mins Matt passes the water bottle back to Naomi with the lid secure as he shakes it. In the next shot the bottle is uncapped as she drinks from it.
Late in the film when Naomi finally exits the vehicle with her daughter, she climbs into what seems like a road with 3-5 feet of snow on either side which appears to have been plowed. The only plow earlier in the film, appeared to be hundreds of metres away. Also, on the opposite side of the snow covered car in the dune, one can clearly see a dug-out area, perhaps for crew to film.
Ice would not have formed in their bottle of water, as that would mean the temperature in the car was below zero. If this were the case, after four hours, they would be shivering from hypothermia.
There is no way the couple could survive for so long without food or sufficient water.
With them trapped in a car covered with ice and snow, holding a small candle toward the top of the window would not allow it to be opened slightly. It would take significant heat to melt the from the top and sides.
In the on-screen text summary in the denouement, 'believe' is spelled wrong. - "Experts beleive they survived due to the 'igloo effect'...".
While trapped snowbound in their car, It seems unlikely that ice would have formed in their bottle of water, as that would mean the temperature in the car was below zero. If this were the case after four hours, they would be shivering from hypothermia.
Naomi's line early on, "Twelve days and two bottles of water. Is that all we have?" It's unclear what she means by twelve days, as she cannot know how long they will be trapped in the car.
After Naomi falls asleep, the baby appears to immediately do so as well, which would not likely occur when the baby had just been crying.
If they were trapped in the car for at least 24 days, firstly on their own and then with a baby, what did they do with all of their excrement and then the baby's.
Earlier the couple made no attempt to use their cell phones. After at least four days days of entrapment, she manages to reach her father. If they had a cell signal, why would they wait for so long to call for help?
Earlier they made no attempt to use their cell phones. After at least four days days of entrapment, she manages to call her father. If they had a cell signal, there is no reason that they would not have tried call for help sooner.