SPN should've had more episodes with haunted water. Don't get me wrong, I love swimming in wild bodies of water. But, at the same time, it's naturally spooky. You're literally out your element, your breathing element, while surrounded by creatures who move through it far better than you can. Like fire or darkness, it brings with it the primal awareness of human vulnerability that powers SPN's backwoods horror stories.
I'd imagine that it's also cheaper than burning down a set, and it lets producers mix in clear shots of the actors' faces. We barely see Peter's ghost in "Dead in the Water," but it's enough. When we see the first VOTW bobbing in water with too much glare and shadow for visibility from the surface, we already grasp that this human is in danger. A lost rope or fishing line could kill her, and then we see shots from the POV of something watching her from below? Alarm bells! The mounting suspense as Sam and Dean appear and disappear while trying to rescue Andrea's kid? Maybe it's an old trick, but I'm not above admitting that I enjoy a classic.
Now, the producers obviously knew that "DOTW" worked. After all, WB specifically invited Kim Manners to become an EP because it looked so good (and, presumably, because it looked so good without breaking its budget). They probably knew, too, that folklore is filled with lore about water and the things that haunt it. There are even quite a few eps where the plot does involve water, from "Pilot" to "Playthings" to "Red Sky at Morning" to "Plush."
For some reason, though, it's the only episode where the brothers have to jump in with the killer. Which doesn't make other episodes bad, but does seem like a few wasted opportunities.
