How does a metal roof conserve water?

If you have a cistern, a metal roof will collect water that can then be directed through piping or a drip/spout process into the cistern, where the collected water is stored for reuse at a future time.

Water collected from a metal roof would be cleaner than water collected from phaIr roofing. Depending on the future u e of this collected water, different types of filtering might be necessary. For "gray water" use (such as irrigation of landscaping), this water probably would be usable without any filtering required.

What if you designed the exposed metal roof to allow rainwater to be directed to a water wall, where it could flow down a metal cascading structure as a waterfall on its way to a cistern?