Is it possible to have a region heal you, or water not damage certain units (which I doubt)?

Yes to the first question, just set a negative-valued damage region.

And if you're thinking about negating the damaging properties of water by putting in a healing region, just remember that the screen will flash red constantly.

Water damages some units?

I have tried that. I had a negative for the base or common amount or whatever and the human or person, but nothing seemed to happen. Should I just make it negative for the human health type?

Remember that the scale for each class means it's multiplying it by that.
And remember that two negatives multiplied by each other equal a positive.
So make sure you don't have both a negative base value and a negative scale factor.

Right! I forgot that little detail. Thanks a bunch!