system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: At times of water scarcity or contamination (say Flint), why can't we make water using hydrogen and oxygen?

Not a chemistry whiz, but hydrogen and oxygen, in whatever form required, could create water, right? Or other chemical reactions that leave water as a by-product? We can harness nuclear energy, surely we can do this?
gpt
This is a little like asking "If polar bears are made of meat, and we can eat meat, why not keep polar bears around with us so we can eat them if we need to?"

Like a pet polar bear, hydrogen is extremely dangerous.  Like a pet polar bear you would need special containment systems in order to carry hydrogen around with you in anything approaching safety.

Like a polar bear hydrogen is hard to get.

Like a polar bear there are better uses we can put hydrogen to than hanging on to it just in case we need to make some water.