The average roof (1000 sq. ft.) will collect over 650 gallons of water with just 1 inch of rainfall. So even 1/8 inch of rain could refill an empty rain barrel.
Rainwater can be collected off the roof by rain gutters and directed into rain barrels. There the water can be stored and used for many non-potable uses such as watering your lawn or the foundation around your home.
While having too much water around your foundation can cause problems, so can not having enough. By hooking a soaker hose up to a rain barrel you can utilize the rainwater to maintain the moisture content in the soil around your home.
Rainwater collection is practiced around the world, especially in areas that are dry or have little access to water. All that is needed is a collection area (the roof), and collection (rain gutter) system, a filtering device (provided on most rain barrels), a storage tank or barrel, and a system to distribute the water as needed (a hose for basic non-potable uses). Some other non-potable uses of rainwater are for flushing toilets, washing clothes, and washing cars.