This isn't the first guy to have found a cheap way to separate hydrogen from water in his garage. See this page: Homemade hydrogen
Anyone can do it.

This kind of thing should be common knowledge. Yet, when people hear about it they oooooo and awwwwww like it's a miracle. There is a reason why this isn't developed. Usually the oil companies buy out the inventor, or give him a cushy job or pay him to keep quiet. If that doesn't work then a campaign to discredit him. If that fails then more drastic measures are taken. It happens more often than not.

Unfortunately, not many people have the engineering and mechanical knowledge to build or convert their own engine. Hence, the technology isn't spread around.