I'm not familiar with a book or novel titled 'Bride for the Water God'. A known series that matches that description, with a similar title and premise, is 'Bride of the Water God' by Mi-Kyung Yun. It's a manhwa, a Korean comic, and its core setup involves a young woman named Soah who is sacrificed to the water god Habaek to save her drought-stricken village. That's the inciting incident, but the main plot quickly becomes more about unraveling the complicated politics and curses within the god's realm, and a massive case of mistaken or hidden identity.
Soah arrives expecting a terrifying deity, but the water god appears as a childish, needy boy during the day and a powerful, amnesiac man at night. The plot digs into why this split exists, the truth about Habaek's past, and the various schemes of other gods and mythical beings in his court. A lot of the narrative tension comes from Soah adapting to this dangerous, beautiful world, dealing with the god's two forms, and uncovering secrets that tie her own fate to his ancient curse. It's less a simple romance about a human bride and more a fantasy mystery with romantic elements, focusing on healing old wounds and the consequences of broken divine promises.
The art is famously lush and detailed, which really adds to the otherworldly atmosphere. The story does have a slow, sometimes meandering pace, especially in the middle volumes where court intrigue takes center stage. If you're going into it expecting a straightforward romantic fantasy, you might find the focus shifts. It ultimately resolves the central mysteries of Habaek's curse and Soah's role in it, but the journey there is packed with mythological references and character-driven drama.