It doesn't use saltwater, or city water, or drinking water, or water of any kind...  It uses hydrogen to power the engine, a technology we've had for a long time now, especially since he was using a hydrogen engine in the first place.  And their claim of no maintenance is pure bull when you consider that the reaction of splitting the oxygen from the hydrogen would leave salts and other mineral deposits in the reaction chamber and on the electrodes thus reducing it's capacity and ability at every use.  That's also if you completely ignore the fact that no matter what, all moving parts and seals eventually break down or the off chance that something wasn't machined or installed properly leading to catastrophic failure of some part of the system, primarily the engine itself.

Granted it looks like a video from the 80's, confirmed by their mentioning the government's star wars program, but the simple fact of the matter is, the industry won't change until their current power source, namely oil, is no longer so readily available, or until consumers no longer are willing to buy from that source.  Also what complicates that engine is the fact that in the mid 80's when he was riding around in that thing, a gallon of gas in the States was under a $1, making that type of engine a novelty at best.

Presently, the reason why he can't sell it is because the auto industry has already spent it's time and money on hydrogen power, and here in California, the oil companies have even been spending money to install hydrogen fuel stations.  Why take the time to screw around with that and buy it when you've already done the R&D for it's real working components before that machine was ever on the news, and already planned for funding and building up the infrastructure to supply the fuel when the time comes to switch to it?  That's why you haven't seen it and wont ever see it in that form.

Like burning ash.

The analogy still works. Ash by itself doesn't give you much energy like just like water. However, using certain techniques you can use ash to create charcoal which is far better then wood at creating heat/energy. Same with water. Put a fire under it (nuclear/coal/oil/etc.) and then use the steam in a turbine to turn a generator and produce energy.

The difference is that water molecules already contain oxygen.  2H2O + O2 ---> 2 HOOH (hydrogen peroxide).  The problem is that producing hydrogen peroxide from water and oxygen isn't an exothermic reaction.  The chemical potential sends it to the water side of the equation.  In contrast you can take Carbon and add Oxygen to it.

Let's assume that you can break water up into hydrogen and oxygen with 100% efficiency, then burn the hydrogen also with 100% efficiency.  What you'd have, at best is zero net energy output.  Of course, it won't be 100% efficient, so instead of having energy generation, what you instead wind up with is an energy hog, a further burden on our energy usage with no gain at all.

There's an old joke that says that the three laws of thermodynamics are:

1. You can't win.

2. You can't even break even

3. You can't get out of the game.

The rule of thumb is that if it sounds too good to be true, it probably isn't true.

sareth got links?