Let me start off by saying that I think Batman Begins is a really good movie. In fact, it is the best Batman movie ever made. It has good characterizations, a reasonably good plotline, suspense, action, a bit of drama… all good movie making.
It does not have good science. Oh, there are good bits here and there. The Batmobile, for instance, is a real vehicle built specifically for the movie, and it really can jump a short distance without a ramp (I’m sure you can look up details online if you’re interested).
It’s the villain’s master plan that’s the real culprit. If you haven’t seen the movie yet (where have you been hiding?) and you don’t want to know the details, you should stop reading this article right now.
The dastardly villain, Ra’s Al-Ghul, has teamed with the corrupt Dr. Crane (aka the Scarecrow) to poison Gotham City’s water supply with a drug that causes irrational fear. The plan is to destroy Gotham by driving the citizens mad with fear and letting them tear the city apart.
There’s a major plot point in the way, though: the fear drug only works when inhaled. That’s why the population hasn’t already gone mad from drinking the tainted water. To complete their evil plan, the villains have stolen a high-powered microwave generator to rapidly boil the city water supply into cloud of toxic steam.
Herein lie two problems. First, why hasn’t Gotham City been overrun by cases of people who have gone crazy after taking a hot shower, boiling a pot of spaghetti, making a pot of tea, etc. There are numerous mundane situations that would expose a person to tainted water vapor, so keeping this evil plan a secret wouldn’t be feasible.
The second and more obvious problem is the microwave machine that they plan to use to vaporize the water. They stand right next to it when they turn it on, causing water in nearby pipes to boil into steam, bringing madness to a portion of the city. Note that human bodies are roughly 80% water: anyone standing next to this machine when it was activated would promptly explode! Nonetheless, intact human bodies remain in close proximity to the microwave machine as the villains try to transport it – running all the time – to the central hub of Gotham City’s water distribution system.
So there are two huge realism issues that you’re going to have to ignore when watching Batman Begins. That’s not so bad really, as long as you know that you’re deliberately suspending disbelief on these issues and not accepting this chain of events as scientifically plausible.