If dowsing has an explanation beyond the ones I have suggested earlier, then it will certainly be related, one way or another, to quantum theories. But I have provided my reasons for thinking that this is not the case.
Despite the weirdness of the quantum world, despite the fact that things are not really where they appear to be, despite the fact that the measured outcome was affect by performing the measurement, and that the observer interferes with the system -- despite all this weirdness, the mad world of the incredibly small does not defy analysis. In that sense, while it may never be fully understood (and it won't, too much is going on, but then the motions of the planets will never be fully understood either) -- while it may never be fully understood, we can at least make significant progress towards trying, using the tried-and-tested scientific method. It seems to me reasonable that the same should be true for anything else in this universe. Therefore, that scientists in the past have tested dowsing numerous times and never found anything worth pursuing is reason enough for me to think that there is little point in any further investigation. However, we're running the risk of going back to the start of this argument again. I've said my bit, you've said yours.
I'd be happy to answer questions you have about Quantum Mechanics -- each "don't know" is related to the difficulty in interpreting the maths, so ultimately the only way to be confident that what I say is true, or not, is in being able to study the maths for yourself.