Did you ever take a bath in the corrupted water before you drained it at that location?
Well some of the corrupted water is still there 
(sometimes its dried up)
Those darker spots in that area is pretty much corrputed ground but the DoT source isnt always visible inside it.
I suggest that you make the DoT spots more visible or change textures entirely..
We considered that, but there are a few problems with that theory.
It doesn’t just happen in dark spots on the ground, you can see that in the video. I have found no visual way of detecting these.
the places on the ground that drained health shift - they do not stay in the same place, even during this one fight. I move several times through areas that hurt me before and then wouldn’t later.
this also happened several times inside the lumber mill and the other place I mentioned, the hidden cave, where, as far as I remember, there never was any corrupted water. And again, there was no visual indication of the ground being different.
If this is the intention, to have pockets of hazardous ground down there, fine. But they need to be clearly visible and visually distinct - which, as the video shows, they are clearly not.
ah, the invisible patches of plagued doom
there is no VFX for it
it’s the most haunting thing ever.
it exists when the area is infected with pestilence, but remains invisible
Well, then that specific pestilence will not be cleansed until there’s a patch. 