Transcript:

So, water is fundamental to life, isn't it? So as an evolutionary trait, normally we should be able to detect water very easily. But there is no olfactory gland in our nose that can actually smell water. It doesn't exist. And there's a reason for it. However, it doesn't mean that we cannot detect water. We can indirectly detect water by smelling a substance that is in water that hits the ground. It's called geosmin. And we can smell geosmin to the level of 5 parts per trillion. It is an extremely small number. Five parts per trillion geosmin we can smell. For comparison, a shark can detect blood about a part per billion. So our detection of geosmin, which is indicating the presence of water, is much, much more refined than a shark. 

So then why don't we have direct smell of water? Because we have a brain. And if you want to detect water, you simply follow an animal like an elephant who knows where to find water, and then you find water. Be smart.