How water-resistant is the iPhone, really?

Some iPhones were advertised as being "water resistant" so I thought that there was no problem with keeping them in the bathroom out of the bathtub so that I could listen to music. Will they be safe? After all, if you can submerge an iPhone under liquid water for 30 minutes, then water vapor, which is filled with similar sized water molecules while having much lower density of water (and hence the minerals that come with the water) should be of no concern. Am I wrong?