The University of Maryland University College notes that one inch of rain water running off from the roof of a 1,500 square foot building produces 935 gallons of water. For some locations, diverting this water is necessary to prevent soil erosion and to prevent chemicals and fertilizers from entering the sewage system. For others, diverted rain water provides an environmentally friendly source of water for use in the home or garden.
Rain barrels are an easy way to collect rain water from the roof and divert it for use in other areas. The University of Maryland University College recommends placing rain barrels beneath gutter downspouts and attaching a regular hose to the barrel for use in watering the garden or washing your car. To prevent water from spilling from the rain barrel, attach a trickle hose to its base and lay the hose around thirsty trees or garden plants.
The Clark County Extension recommends diverting roof rain water through a gutter downspout and into a dry well for slow release into the soil. Dry wells are small pits placed approximately 10 feet from buildings. They are lined with a water permeable fabric or plastic that slows the passage of water into the soil, and some pits have an inch or two of gravel at the bottom. Dry wells collect roof rain water and slow its release into the soil, preventing erosion and keeping the surrounding soil moist but not water logged.
The University of Colorado at Boulder describes grassy swales as a low area of land planted where water flows due to gravitational pull. Planted with native grasses or plants that slow the movement of rain water, allows the plants in the swale to receive water released in a measured manner to the surrounding land. Roof rain water can be diverted to a grassy swale through a pipe attached to the gutter downspout. The pipe can run above or below ground.
Rain gardens or bioretention facilities are similar to grassy swales, but they are a water feature that uses native plants to add interest to the landscape. The University of Wisconsin-Extension estimates that a rain garden allows approximately 30 percent more water to filter into the ground than a lawn does. Rain water is diverted from the roof through an above- or below-ground pipe and captured in the rain garden, where it waters the native plants and is slowly released into the soil. Rain gardens might also be lined with permeable fabrics or plastics to further slow water filtration. The Environmental Protection Agency notes that the slow filtration action of a rain garden helps remove pollutants from the water before it reaches waterways.
The Clark County Extension recommends using french drains to divert roof rain water to ponds or a perforated pipe system to slow the water flow. A french drain uses a perforated pipe placed in a gravel filled trench to direct water flow while allowing slow seepage along the drain’s path. The downspout from a gutter system can be directed underground and into the french drain system.