> Pure water electrolyses if you try hard enough. It's just silly inefficient.

You have to be trying really really hard though. There's a classic demo where you can make water maintain a bridge between two beakers, by putting a decent few kV across it. You need to use extremely pure water to avoid electrolysis, which is pretty successful.

> > Table salt is normally not used by people doing electrolysis. Other salts such as sodium/potassium hydroxide, or if nothing better is at hand, sodium (bi)carbonate, are safer, similarly cheap, and also do the job better.

Well.. It's actually pretty common, but not for when people want to make hydrogen. The Chloralkali process (i.e. NaCl hydrolysis) is the primary industrial method for producing tens of millions of tons of chlorine and sodium hydroxide.