It's not really air that powers the car, but pressure. You can't usefully compress water, but you can generate hydrogen from it with enormous amounts of electricity. When you hear people talking about 'hydrogen economy', they're mostly talking about hydrogen from water. Then you can transport the hydrogen and keep it in storage until you need to use it. When you burn it, you produce water again - totally non-polluting!

The big problem for the nations who use the most fuel is dual - no water and expensive electricity. Malaysia ought to be at the forefront of developing these kinds of technologies - plenty of water and too much power from the sky. But you still have fossil fuels, which are a marvellous commodity to be long in right now. No need to work hard!

You could probably run your remote control car off air right now - just buy a can of compressed air (like for cleaning electronics), and adapt the throttle servo so that it pushes the valve in, then fit a paddle wheel on the back axle - it might work quite well. Maybe not much torque for starting. When you see the videos of the French-designed air car it seems like there's no torque for starting either, but I'm fairly sure it uses pistons to convert pressure to torque.