The characters are worried about live electrical wires touching the water, yet to turn it off they flip a switch already underwater. This would mean that the water is already conducting electricity in the first place.
When the underground garage of the supermarket is flooded, several people remain in their cars and vans for more than an hour without leaks, and the cars don't float. In reality, cars that are submerged up to the roof become totally flooded within 1-3 minutes. Occupants have less than a minute to get out, otherwise they will drown. If the windows are shut, a car will tilt up and sink front first.
When the supermarket gets flooded, the floating rubbish consists of mainly empty bottles which would have had to have been empty prior to the tsunami.
Lifeguards at Australian beaches would have spotted the shark before the attack due to the shadow cast by the creature in the water and used walkie-talkies and/or hand signal to communicate to the lifeguard on the jet-ski there was a shark nearby.
After the tsunami hits the supermarket, the camera pans over the devastation and passes over the top of the shelves with debris washed up on them. It shows a pair of thongs sitting upright and next to each other like someone just slipped them off.
In the scene where they provide oxygen through the tube and the character has run out of length, they pull the whole tube back, just mere moments after the power shut off. Less than 30 seconds had passed since he took the big breath and only 10 seconds after the power was shut off, the girlfriend asked "where is he".
Had they not pulled the tube back, he may have been able to reach it before his oxygen ran out.
Had they not pulled the tube back, he may have been able to reach it before his oxygen ran out.
Steven's death, though heroic, was completely avoidable. He was only about a foot away from reaching the electricity cut off lever, when the oxygen tube ran out of length. However, the characters holding the tube above water in the main hall had more than enough shelf-space to walk on. Even before Steven felt he had to remove the tube to reach the lever, those characters should have moved to the other end of the shelves to give him as much slack in the tube as possible.
At the end when Josh emerges outside from the supermarket his t-shirt is completely dry despite being completely wet just seconds ago when still inside.
The accents jump from Australian to American.