What happens to the water draining from your roof? The water either goes into your plumbing waste system through interior roof drains or into the landscape around the building via scuppers, gutters and downspouts. Any water coming down the side of the building should be controlled to prevent erosion of the wall or erosion at the bottom of the wall. Re-using that rain water is gaining more interest. It can be piped to water the landscape or even stored in a tank and re-used for non-potable water uses inside the building. See the following site for a more complete description of the issues – en.wikipedia.org/wiki/Stormwater.