system
Given the following post, respond as if you're commenting on Reddit:
human
Can water really be broken down and used as fuel? If so, why aren't we using water as fuel for everything?
gpt
We don't use water as fuel because it isn't a fuel. Hydrogen is a fuel, but you only get it by breaking water, and the energy released is necessarily less than you put in. So in this sense water/hydrogen are being used like a battery.

There are several economic reasons for restricted adoption of hydrogen storage, like the explosive risk, need to compress, metal embrittlement, and cost of fuel cells.