Oxygen can be extracted from water in a process known as electrolysis. Water molecules consist of two hydrogen atoms paired with one oxygen atom. Connecting two electrodes to a power supply and placing them into salted water allows an electric current to flow. Electricity is the flow of electrons, therefore one of the electrodes – the cathode – becomes negatively charged due to the buildup of electrons, while the other – the anode – becomes positively charged because of an electron deficit. This difference in charge causes water molecules to separate into their constituent parts, with oxygen bubbles appearing on the anode and hydrogen bubbles accumulating on the cathode.
Might we one day be able to ‘breathe’ in the water? To do this, humans would need a system similar to fish gills in order to harness dissolved oxygen. All water in contact with the air will contain a small amount of dissolved oxygen – around five millilitres (0.01 pints) per litre (2.1 pints) – and it is this oxygen that diffuses into the bloodstream flowing through gills. It’s impossible to know if humans could ever ‘evolve’ gills, however it is unlikely to serve any practical use since there is plenty of oxygen in the air.
Answered by Rik Sargent