The biggest question is, how did a million people travel the desert for 40y without water. If you remember, Aaron had to strike his staff against the rocks to create water, once. Supposedly 1M people and their livestock drank and washed from a single magic stream, moved and ... struck the staff against the rock again? No, because when Moses did that, God got so angry, Moses was forever banned from entering the Promised Land.
The logistics of the story alone are absurd. By the time you have moved that much people even just a mile down the road, they would've all died of dehydration or starvation.
Also God said that the rock will yield water. In ancient times, it was indeed understood that rocks contained water (because they often had 'springs' originating from between rock structures). God did speak a falsehood when he said the rock would yield its water because as we know, rocks do not yield water, they do not contain either hydrogen or oxygen.