The memory of water / Karen White.

Enhanced descriptions from Syndetics:

The New York Times bestselling author of the Tradd Street novels returns to the South Carolina Lowcountry with a gripping tale of two sisters haunted by one tragic night...

On the night their mother drowns, sisters Marnie and Diana Maitland discover there is more than one kind of death. There is the death of innocence, of love, and of hope. Each sister harbors a secret about that night-secrets that will erode their lives as they grow into adulthood.

After ten years of silence between the sisters, Marnie is called back to the South Carolina Lowcountry by Diana's ex-husband, Quinn. His young son has returned from a sailing trip with his emotionally unstable mother, and he is refusing to speak. In order to help the traumatized boy, Marnie must reopen old wounds and bring the darkest memories of their past to the surface. And she must confront Diana, before they all go under.