Specialization Purviews Water
Yours is the power of the sacred rivers, from which divine blessings and mortal bounty flow. The specialized River Purview belongs to deities specifically associated with a specific river or rivers in general, rather than all waters, like Oya, Òshun, Sarasvati, and Sobek.
Drawback: Your water marvels can't create or manipulate lakes, oceans, or other non-fluvial water.