It’d be really useful if we could breathe underwater. It means we could not worry about drowning in the sea and everything, or swimming pools for that matter, but it’s really difficult because we are obviously land mammals and our lungs adapted to taking oxygen out of the air.
So we breathe in, and the oxygen’s taken out of the stuff we breathe by the blood and it goes around the muscles and things. And fish breathe underwater in a sort of similar way in that the water goes through their gills, which is the equivalent of their lungs, but they’re not taking the oxygen out of the water itself, like the H?O that makes up water. What happens is they’re taking the oxygen that is dissolved in the water. So the water dissolves oxygen from the air and the fish gills can take that out.
Unfortunately, there isn’t that much oxygen in the water. So the fish gills are really well designed at coping with that and putting lots of water through to make sure they get enough oxygen. And, simply, if we breathed in water somehow there just wouldn’t be enough oxygen in there, even if we could take it out, to service the amount of oxygen we need. So that’s why we can’t breathe underwater.
And I think also it would be quite unpleasant because, you know, water in your lungs, have you ever had that? It’s horrible.