What is the significance of collecting water from the church in geomantic omen?

In geomantic omen, what does this hall mean by gathering water-any terrain is composed of mountains and basins. A small basin in a mountain is called Tangju in geomantic omen, and this hall also refers to such Tangju. The water in this hall, that is, the running water in the hall, includes the terrain with natural intention of running water when it rains.