I'm seeing your effect isn't just "move a torrent of water," as suggested in ArM5, page 85, right column. It's more of a:
Neptune's Prison ReAq 30 (Base 10+1 voice + 1 concentration + 2 very unnatural) (but I'd be willing to accept a Base of 5 if the couldn't move quickly)
Coalesce and hold a sphere of water with a radius of ~5 feet. (1.5ish paces) Move it at your direction for as long as you maintain concentration. It swirls and spins with an internal current.
Sure, I guess it could just pass over the magus if it failed to Penetrate, leaving him unharmed and may or may not make him wet. It might lose a little volume. Both points are totally cosmetic and I guess I'd worry about it if the story needed me to worry about it. I could also have it slide around him, never touching him, if it failed to Penetrate. Neither one matters, because if the effect fails to Penetrate, then it doesn't effect the magus.
The globe does what ever you want it to do, distorting, not distorting, losing volume, fitting or not fitting. Regardless of what it does, it doesn't affect the magus if it doesn't Penetrate.
Sure, it can get the magus wet, if that fits. But in that case, that's normal behavior for what is essentially a magically thrown bucket of water. You're not describing that, at least not to me-- I'm seeing something like the sphere of water in HP:5 and the brawl in the Ministry of Magic, that's why I'm providing a sample spell for us to discuss. If you just want to magically throw a bucket of water with the crazy intense force to cause damage, then sure, it makes sense for the magus to get wet if the effect doesn't Penetrate. If you wanted to fling the water and make a targeting roll, then I'd warrant that the water isn't resisted and doesn't need to Penetrate, but I'd also say you'd need to lobbing more than a cubic pace to do more than knock the wizard prone and that judgement would likely be completely troupe dependent
But all of this wanders into odd, undefined territory, unless you want to get crazy mathematical-- and some people enjoy that.
What is it you want to figure out? Can you kill a magus by deprivation if you throw a sphere of magically-controlled-yet-mundane element over him and hold it there?
I guess? Maybe? If he just sits there when you do it, but I don't think I'd let it happen as a Storyguide. Really? That's your plan? Put the equivalent of a pillow over him if he can't move, so he smothers? Otherwise, the benefits for form base bonuses are there in ArM5, page 78.