Nerogorath

Hello there I recently had a idea for a house mod but I want to add in a small lake somewhere higher up. Whenever I used water before I only set the water height and lowered the terrain to water level when needed. As I can't lower it without making a huge crater how do I add water or raise the water level in a certain area? It has to be possible somehow because it's already in the game. And I checked it it's not faked it acts like real water.