This is a Fantasy book either Children's or YA. The cover has a picture of a girl of East Asian descent surrounded by water and maybe tentacles and the title had Water in it.The summary had something about a mysterious stranger, a girl , and a talking horse. The author of the book is a woman and I believe this came out between 2007-2013?The main character is a girl who is hiding as a child running from this evil aristocrat lady who uses magic to create cancer or a disease from people's hair strands to kill them. There is a guy with a talking horse who helps the main character as well as an older woman who helps her uses her changeling powers. They are seeking help from this underwater king who is like an octopus.
Her first new novel since The Margarets, The Waters Rising marks the glorious return of the extraordinary Sheri S. Tepper, the award-winning contemporary master whom Locus has called, “one of sf’s most distinctive voices.” The Waters Rising tells a gripping story of a future already ravaged and now in even graver peril when a dreadful, awesome killing power is resurrected  Her first new novel since The Margarets, The Waters Rising marks the glorious return of the extraordinary Sheri S. Tepper, the award-winning contemporary master whom Locus has called, “one of sf’s most distinctive voices.” The Waters Rising tells a gripping story of a future already ravaged and now in even graver peril when a dreadful, awesome killing power is resurrected from the past. Readers of Margaret Atwood and Marge Piercy will join with fans of literary sf in praising this stunning masterwork of speculative fiction from one of the acknowledged greats. ...more