Most often, water represents cleansing, life and freedom. Water is a contextual symbol in literature, however, meaning that it can symbolize many things depending on how it is used in a novel or a story.
Often, the type of water in a story or novel is just as important as the fact that water is used as a symbol. Rivers often represent the flow of life or fertility. Rivers are typically used as symbols by authors because rivers flow; they are constantly moving and they follow a distinct path.
Oceans, on the other hand, because of their scope in relation to the earth, often represent obstacles or abysses from which things emerge or that characters must journey across to reach a destination. Oceans are often symbolically mysterious places that can symbolize overcoming a great obstacle or being dragged down into deep depths by it.
Lakes are often used as symbols in tales in which characters face great decisions or much introspection.
Water generally cleanses, however, and it inevitably becomes a symbol of characters in stories handling difficult life scenarios. In any case, water is a symbol of power in stories. It has the ability to free characters as well as claim them.