Lasers would be the best choice. Rail guns would be a good solution in low gravity/thin atmo situations. When I wrote that I wasn't thinking about the problems with using rail guns out of a deep gravity well with dense atmo. I assume that is why you say rail guns can't put anything into orbit.
Lasers can't put anything into orbit, either.
Either could (theoretically, neglecting the problems with being a burning ball of plasma) launch something to orbit altitude, which is not the same as putting something into orbit. The problem is that you've got to apply another large delta-V at some point and in the right direction, to actually put the vehicle in orbit.
Best case from the flaming ball of plasma perspective is to launch straight up -- which happens also to be the worst case from the perspective of applying a delta-V to put the thing actually into orbit.
Best case from a delta-V perspective has you launching at a pretty low elevation angle, which roughly doubles the amount of atmosphere you'd have to be a flaming ball of plasma in.
Assuming you surmount that problem, there's still the problem of getting the water from where you put it in orbit, to a position where it can be loaded into your space ship (which, in a practical sense, means your target vehicle will have to do the rendezvous).
You've no doubt spotted the fly in the ointment here: how much delta-V (and how much propellant) will have to be expended just to fuel your water-powered space ship?
Note, too, this little nugget:
McConnell envisions space coaches cruising around the solar system, each individual vehicle fueling up with water in low-Earth orbit when the need arises. In the future, fuel could be sourced along a space coach's travels — for example, water could be mined from an asteroid or a Martian moon.
Yup .... all you've got to do, is just pop out of that interplanetary trajectory, down into Low Earth Orbit; or, into the orbit of an asteroid or a Martian moon.....
How? Does our author understand the orbital mechanics of his "simple" solution?