Residential feng shui said that "the incoming water should be bright, and the outgoing water should be dark". How to understand it?

In the speech of residential geomantic omen, "the water should be bright and the water should be dark". How to understand it? -"Water is bright, Tianmen is open, and the road to wealth is wide." Such as rivers, it is best to indicate the location of the water inlet; On the other hand, it is understood that the obvious water flow is a small river flow, which is easily blocked by other objects; Throughout history, rivers are home to great dragons and caves, and streams and small waters are useful and small. "When it got dark, the land was collected and the money was collected." Generally, the nozzle is tightly controlled, that is, the water is dark and the door is closed.