I am having a hard time finding data on the density at the Veneral orbit. It seems to vary from 10ish to 3 H+'s per cm^3 at earth but has got to be thicker further in.
I'd probably only double the density for Venus, if that... you're still pretty damn far away from the sun.
So between 20 and 6. Even assuming complete efficiency (heehee) my magnet array would have to be miles across to get a mol a second of water. At least I know how to power it.
That sounds just about right. Still, that's 3.6 Liters of water every hour, provided you could find a way to make it work. You might be better off extracting the existing water vapor from the Venusian atmosphere. It's on the order of what the Earth has to offer, but doesn't cluster up (like clouds), as far as I know.
A lot of it is heavy water because of the differential loss of protium. The heavier Deuterium is harder for the wind to blow off. Heavy water stops eukaryote cell division. I think even Venus's tail which is much richer should be avoided as its H is bad H. But maybe 5% deuteriation is exceptable.