Exodus 15:22-27 gives us great insight to the wonders of history, or more importantly, how little Bronze Aged people cared about recording history.
It begins with Moses leading the Israelites from the Reed Sea into the wilderness of Shur. But much to everyone’s surprise, there isn’t much water to be found in the desert. With temperatures rising, and bota bags shrinking, the Israelites pushed on to Marah. Unfortunately, when they reach Marah, they find that the water there is bitter! Thus, they named Marah, Marah; because Marah means bitter. I know the chronology is a bit off, but that’s the bible’s fault, not mine. I’m assuming we’re expected to understand that Marah had a different name prior to them naming it Marah, and the author just called it Marah prematurely.
Now, we can choose to believe that the Israelites went on a naming spree as they traveled, but that’s a bit far-fetched. The more obvious explanation is that the bible is creating a neat story. Historians see these types of legends so often that they’ve created a name for them—they’re known as etiological myths. They run the gamut of rather dull origins, like the names of places and objects, to the more colorful ones, like how the leopard got its spots.
Anyway, Moses listens to the whining Israelites (now is not the time for a racist Jew joke) and cries onto the Lord. Luckily, God tells Moses about a magic wood that can be thrown into the water to make it sweet. To which, we probably have another etiological myth. You see, berberis has long been added to brackish water to make it more palatable, but nobody knows who first thought to add it to water. Nobody, that is, except THE BIBLE!
So, after teaching the ungrateful Israelites how to make clean (at least clean tasting) water, God makes a deal with the Israelites. He tells them, that if they listen to his words, and if they do what he tells them to do, he won’t annihilate them with plagues, the way he wiped out the Egyptians. Well, isn’t that sweet of him. Of course, I should point out the unspoken flip side, that if you don’t listen to God, he will seriously mess you up!
There is also an inconsistency between the camping locations of Exodus and when these locations are repeated in Numbers. Exodus tells us that they moved into the wilderness of Shur to get to Marah, but Numbers 33:8 has them continuing through the wilderness of Etham to get to Marah—never mentioning Shur.
Finally, the Israelites reach Elim, where there are twelve wells to draw from. Ah numbers, that means it’s time for math! If there are 2,000,000 Israelites, and each person needs 1 bucket of water a day, then each of the 12 wells will have to be drawn from 166,666 times. Assuming each draw from the well takes 1 minute, then we’re looking a total of 116 days to draw enough water to hydrate the entire group. We would have to at least double that in order to account for all the livestock, which means we’re nearing a year for one day’s worth of water. Even if they could draw 25 buckets a minute per well, it would still take over 9 days to draw the water, at which point, the people waiting in line would already have died from thirst.
None of this is in the movie.