The writer of the stories that inspired the movies for Ring and Dark Water has been discussing his stories, what inspires him, and more importantly the film adaptations of his books. For those of you who don't know, his name is Kuji Suzuki, and the stories are quite different from those adapted to the screen.

From Nich Bei Times:

While Suzuki’s sequels took its characters into biology and computer labs, the film sequels did not follow suit.

An adaptation of "Spiral" was produced alongside "Ring" with a different director and crew, then released concurrently....The studio hoped that the films would generate interest in each other, but no such thing happened..."Ring" became a cultural phenomenon and a sequel —which completely ignored the events in "Spiral" — and was crafted to capitalize on the success. That sequel, titled "Ring 2," merely rehashed popular scenes from the original and went on to sizable box-office take.

I've never seen Spiral but I have read the novel Ring which has some surprising differences and really turned me on to Asian horror writing. However the movies seem to have gone their own way, and although Suzuki isn't happy with the direction of the films it looks as though he has a chance:

"There is talk of me writing the script to (an American) sequel based on 'Spiral.' In America they’ve made the (films) 'Ring' 1 and 2. The second one was not based on any story and was weaker. If I get to write the sequel script, it will follow 'Spiral' very closely."

That indeed would be interesting to see, but it would depend which director is married with him.