Collecting rainwater for reuse is a centuries old method especially in areas that don’t get much rain. The most common method for water catchment is to add a covered reservoir to an existing building’s gutter system thereby directing rainwater into the reservoir. This enables thecollection of a larger amount of water than say putting out a bucket in the yard during a rainstorm. It also affords protection to the collected water from mosquitos and other larger debris. You can use this water to water your gardens, plants and lawns cutting down on a substantial amount on your water bill. While you can build your own collection system, easy to install fabricated collection systems are becoming more and more popular with major retailers.
See the following articles and resources for more information:
An Introduction to Rainwater Harvesting
How to Build a Rainwater Collection System
Not Your Grandmother's Rain Barrel
http://www.rainwatersolutions.com/ in Raleigh/Durham