I have set up a lunar base with around 500 people. Cargo shuttles ("Bullets") regularly fly up and down from low lunar orbit. These shuttles, unfortunately, have a very high mass ratio of around 6 because of their propulsion system. Water is the cheapest available propellant, being present in quantities up to a billion tons in the Moon's polar craters. So the Bullets use superheated steam as propellant (being much safer than hydrogen-oxygen chemical as it avoids the obvious explosion risk). Although this allows a very fast turnaround, a nuclear reactor powered steam rocket will only have a specific impulse of ~195 seconds. Thus, every time the shuttles want to land or launch to deliver, say, 10 tons of cargo, they are sending dozens of tons of water spewing out the nozzle and into unrecoverable lunar orbits.
So, the dilemma in a TL;DR: How to avoid losing many tons of water, which is vital to conserve as much as possible?
Now comes my proposed solution. Due to the low specific impulse/exhaust velocity, much of the ejected water will be in orbit around the Moon. Therefore, it would still be accessible... if, like Earth, the Moon trapped the molecules in a magnetic field. Obviously, it does not exist. So what if the lunar base crew set up an artificial magnetic field, much like a Bussard ramscoop, to capture magnetized ions of water and bring them down to the lunar surface?
With sufficient power for the generator, would the above scheme to capture water for re-use be feasible?
It does not necessarily need to be fast or short term. I am only asking if it is possible.
I appreciate your feedback and answers. Thank you!