Intelligent Design

[ErGingerbreadMandude]

Yes, Pool..is does answer the why, completely and with nothing left to explain.  You can only get water with h20 because that's what we've defined -as- water.  If you use some other chemical structure, you get other substances which we have defined as other things, as "not water".

Next, please.

There was hydrogen atoms and oxygen atoms and water before we defined them as hydrogen atoms and oxygen atoms and water.

 You can only get water with h20 because that's what we've defined -as- water.

Is wrong because even if we didn't define what we got from h20 as water we'd still get water. We don't get water because we defined what we get as water, we get water because it was how it was designed.
Just like in the case of 1 + 2 = 3 , we get that result not because we defined the result as 3 but because of the design we enforced in the number system and addition operation.