What would water and fire do to the Nazgul?

[Voralphion]

Remember Elrond has the Ring of Power, the Water Ring

No he didn't. Elrond had Vilya, the ring of air, Galadriel had the ring of water, Nenya.

I believe one of the reasons the Nazgul feared water was because Sauron had no control over it. Throughout middle earth, water represents something pure and good. Even in tthe first age wateer kept Morgoth from doing many things because of the power of Ulmo. I think the same is true here, it has to do wih h power of ulmo.