Water: Tales of Elemental Spirits is a book of short stories, half by Robin McKinley (author of The Hero and The Crown, etc) and half by Peter Dickinson (author of Eva). The stories are linked in that they are all about water and about fantastical creatures that live in water. The stories were otherwise, though, not related to one another and were stylistically different. I could tell without even looking, though, which ones were McKinley's, as I think she has a very strong voice (I've mentioned this before, in my review of Sunshine).
Mermaid Song by Peter Dickinson: Great little story about a Puritanical village whose women have been keeping a secret for generations. Sad, but has an ultimately hopeful ending.
The Sea-King's Son by Robin McKinley: A fairy tale about a young woman who falls in love.
Sea Serpent by Peter Dickinson: My least favorite of the stories, as I just didn't quite get what was going on, to be honest.
Water Horse by Robin McKinley: A girl is apprenticed to learn how to be Guardian, one who keeps her island home from being taken back by the water. Reminded me, for some reason, of Ursula LeGuin's Earthsea books.
Kraken by Peter Dickinson: Loved the dual nature of this story, about young lovers and the mermaid who helps them.
A Pool in the Desert by Robin McKinley: Fans will be pleased to note that this story takes place in Damar, home of Aerin and Harry (although neither of them appear).
Buy Water: Tales of Elemental Spirits on Amazon.