SciFi and Fantasy Book Club discussion

I can't remember what it's called, or the author's name, just a vauge-ish description. I can only half remember what it's about, I read it when I was in elementary school, so'd be maybe 8-10 as best as I can figure a timeline. I had a copy once, but lost it or something.

Despite how old I was when I read it, it wasn't a kids' book. The copy I had was paper back, about 3inches thick, blue-ish green cover depicting a waterfall and fern-like vegetation on the rocks around it, at night. I think there were people hiding in the bushes as well. The title was in a fancy silvery script at the top, and a similar font was used for a smaller authors name at the bottom, though I can't remeber what the words say. The spine was blue, with the title and author printed over again, and I believe the back was blue with the descrpiption in white letters, in a longish paragraph. As per plot and characters, my remeberance is even more vauge than it's apperances. It was a fantasy novel, that much I recall.

I know as well that:

*the characters seemed to live in the shadow of a volcano
*said volcano was said to hold a fire goddess, to whom there were nun sort ladies devoted
*they live in caves in the side of the mountain
*one of the main characters , a man and fighter, comes to seek refuge there when injured
*he was fighting against some sort of water wizard sort antagonist
*the hydrowizards are sorta trying take over
*they build their hideouts/ castles out of water, and often change around the rooms since they have complete control over water
*they also have assasins with curved daggers made of water
*injuries from these blades never heal
*the guy that was seeking refuge was cut by one of the water daggers, fighting against the wizards (or their underlings more likely)
*another main character is his love intrest, a strong willed seer-is(I think that's what she was)
*at some point she leads a funeral pyre, since they burn their dead
* there are also people who live their whole lives at sea
*they all get wiped out except one boy(another man character) who finds out he's apparently the sea godess's consort
*to avoid getting dragged into the sea to be with her, he goes ashore
*that breaks his peoples every rule basically, but he's the only one left, so he doesn't care
* he has a talent for finding streams and whatnot
*he helps the fighter guy out, and heals him, even though he was hit by the water dagger(wounds from which aren't supposed to be healable)
*he thinks it's just the cauterization, but it's his consort powers he doesn't know he has
*the last main character is a lady leaving her abusive husband to join the plot against the hydrowizards, it was kinda a subplot
And I think they were about to fight the hydrowizards, but that was going to be in the next book. The author said they wanted it all to be in one book, but her publisher made her split it up into two. Any idea to the title?