>Interesting, yes... But is it a good idea?? If we can use sea water for our engines, it´s ok. If not, maybe could be a trouble...
>
>http://www.globalpolicy.org/security/natres/water/2005/0829waterwars.htm

As far as I can understand, the electrolysis can't really be done with pure water - but a saline solution is OK. So, the engines burning 2H2+O2 may produce pure water out of sea water as a side effect.

It's more the cost of electrolysis that's the concern. If only solar power could be used for that, we may be onto something.