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?
That could look great in the rain, of course, but what about when it's not raining? Rather than diverting roof water to a cistern immediately, the water could stay collected on the roof to continue flowing after the rain, extending the natural process to be enjoyed at a later time.
Such a system could use the roof itself and a water collection system. This stored tray of water sitting on the roof would be like a pond contained in a metal tray. The stored water could offer added benefits: It could help protect the building from solar gain, while helping control the internal building temperature.
You could look at this as a multi purpose system that offers a number of benefits:
Protecting the building from solar radiation
Slowing water from entering the public water reclamation process
Cooling the local atmosphere
Creating a water park on the roof for building users and views from other buildings.
All of these are just ideas, of course, but by using collected water in new and varying ways, you maximize its possible uses. While taking full advantage of the earths natural process called rain. The reuse of one element in many ways at the same time is the key to conservation. We are all designing buildings that use elements in many ways. If we can design using the same element in many ways, we are truly conserving products, elements and energy.
By thinking and dreaming, we can achieve multiple uses of one element - such as the water collected by a metal roof. Use it! Turn it into something that is multidimensional in its use. Expand the thought process. Let your mind do all the work, and then create unified uses with fewer materials.
Have fun designing with metal roofs. Think of the multiple uses that can be achieved.