I was wondering about the hydrazine scene as well, not because you can make water with it (you can) but because the stuff is scary dangerous. The slightest whiff of fumes is very very bad for you. But strictly speaking, you can get water from it.
Hydrazine isn't quite
that scary, but definitely not something you play with. Most steam power plants use hydrazine solutions as an oxygen-scavenging corrosion inhibitor in boiler water. Straight hydrazine is used in F-16s for EPU operation. I think the hydrazine burning presentation in the movie was reasonable. I did like the scene where Whatney got blown up and later sits down at the computer station, still smoking with his eyebrows singed. Funny, funny scene.
I do want to sit Andy Weir and Ridley Scott down and give them a stern lecture on gas laws and static and dynamic pressure. The sandstorm damage and tilting of the MAV were both impossible, but I understand Weir had to have a scenario that made Whatney a castaway, and it had to be done by Mars (vs. a man-made equipment malfunction). I can't think of another semi-realistic scenario that would do the trick, so I'm willing to look the other way on that. However, patching a 10+ ft diameter hole in the Hab with clear plastic sheeting and duct tape was just ridiculous and could have easily been done better. 14 psi differential multiplied by 10,000 square inches = 140,000 pounds on your plastic and duct tape repair. Result - instantly popped Hab. Had they handwaved some thicker canvas and some super-awesome NASA adhesive I might have been OK with it, but clear Visqueen and duct tape was just wrong.
The pristine condition of Pathfinder and the LEDs and the big ON button on it bothered me, but whatever.
Beck bouncing around on the exterior of Hermes without a tether was just stupid - even people not versed in spaceflight operations know that he should have had tethers. That drama wasn't needed and was an obvious inaccuracy.
The Iron Man scene was just ridiculous. When it was mentioned in the book I knew they would tinker with it in the movie, because Iron Man!, but I think a rescue as presented in the book could have easily been done with the same degree of drama and much more realism. It was just too over the top, turning a dramatic moment into an "Oh WTF!" moment.
I also think the equipment was too futuristic looking. The computer displays looked like they were recycled from the Star Trek Next Generation set. I really was hoping for things to look more near-future, equipment and computers a little closer to what people are familiar with now. It's hard to describe, but a lot of the props struck me as being from a campy sci-fiction movie from another universe vs. something plausible in our near future.
I almost wish they would come out with The Martian - Nerd Edition for scientists and engineers, and leave the regular Martian for the masses who may not be bothered by these details. Maybe even tie it in to current technological development efforts (like MIT's MOXIE experiment) which actually are leading to the technologies seen in the Martian.
OK...I'm done. It was a good movie, really funny in a lot of spots. I enjoyed it immensely. I think it did a good job of pitching a science-based story to the crowd.