Yeah, it'd probably be worth less than a real one because that kind of damage could be faked so easily, buyers would be very skeptical. (not saying you did it, but that is what people would naturally assume)
But it is very strange. Because when a card gets wet, nothing like that happens. The foil on the card just comes off the back in one piece, it doesn't wash away like that.
But as far as I know it is normal for all holo cards to have foil underneath parts that normally wouldn't look holo.