My theory: I think maybe the tap water was hardening the emulsion somehow (maybe?) or something to that extent. They're too regular to be chemical stains. I think that if the emulsion was softened unusually so that you could have damaged it by touching it.

Did you examine the marks up close? That way you could see if it was a depression or movement in the emulsion (which would leave it to be caused only by the gloves which we might be able to backtrace to distilled water via softer emulsion) or a residue (which should wash off and cause by powder or drying chemicals).