They consist of a storage container (usually plastic), a system for diverting downspout water into the barrel, and an overflow that returns to the downspout or diverts water safely away from the house to absorb into the soil.
They should also have the following:
Rain barrels are good for collecting water to be used in dry summer months. If water is diverted into the yard, they work best for soils that drain well (such as the eastern metro region) rather than the west side where clay soil is hard and less absorbent.
Rain barrels are also well suited for areas that operate a combined sewer system like Portland. In Washington County, we have two separately piped systems: stormwater pipes that lead from the outside of your home to storm drains and eventually the Tualatin River and sewer pipes that carry your used wastewater directly to one of our four treatment facilities before it is released into the river. An additional benefit to our separately-piped system is our Surface & Stormwater Management (SWM) program that provides street sweeping, leaf collection and bioswales in new development that help minimize the pollution that enters our local rivers and streams.
You should consider how much rain falls in on your roof. Just one inch of rain falling on a 1,000 square-foot roof produces 625 gallons of water. With an average annual rainfall of 42 inches in Oregon, you have 26,250 gallons of water falling onto your property each season. You'd therefore need to install 525 fifty-gallon barrels to contain that rain. More importantly, rain runs quickly off of our hard clay soils here in Washington County and can cause flooding to you or your neighbor's property if not piped correctly into our stormwater system.
If you do choose to install a rain barrel consider disconnecting the barrel during the winter to avoid constant overflow during the rainiest months. Attach it in the early spring to fill it for use. Like any irrigation supply dependent on rainfall, sometimes you’ll have too much and sometimes not enough.
We encourage your efforts to keep our water clean. Instead of disconnecting downspouts around your home, here are other steps you can take to protect clean water:
Plant natives: Removing water and chemical-dependant lawns and replanting with native plants filters out pollutants and stabilizes your yard. Use a Native Plant Finder to choose plants that are right for your yard.