Seventeen-year-old Christina McBurney, grieving the loss of her twin brother, Jonathan, to consumption, has run away from her Parkdale home. She believes her mother wishes she had been the one to die, and she plans to find work far away as a nursemaid or teacher. Christina's cousin Peter is the first mate on the Asia , a steamship that transports passengers and freight throughout the Great Lakes, so she seeks him out to secure passage to Sault Ste. Marie. But when a violent storm suddenly rises, the overloaded and top-heavy steamship begins to sink. Christina, heeding the warnings from her cousin, somehow makes her way to the hurricane deck. A large wave tosses her overboard, but just before she loses consciousness, she is pulled to safety. Hours later, adrift on the wide-open water of Georgian Bay, in a lifeboat full of corpses, Christina is nervous about being alone with Daniel, a brooding young man with a likely criminal past and the only other passenger left alive.

But they both know that working together is the only way they will find the strength to make it to safety. Big Water is a fictional account of the real-life story of the only two survivors of the sinking of the SS Asia in 1882.