I have a cell (my dungeon) and im trying to add water, but my cell doesn't have a location. what should I do?

What do you mean? You want to place water into an interior? Just use one of the water objects. Look in vanilla dungeons to get some names (Of the various types of place-able water), then find them in the object window and drag them into your world.

so, i see water falls. i want to flood a part of my nordic big room. how would i do that?