Question: why are we 70% water

Chris Cole answered on 14 Mar 2014:

That’s almost a philosophical question. It would be so much better if we didn’t need to carry around all this water sloshing around in us.

I think it stems from the fact that all life an Earth originated in the sea. The first simple organisms were sacks of water floating around in the sea. These became cells – the building blocks for all life – which have clumped together over billions of years to make more and more complex creatures. Like us.