It hard to imagine in February that Spring, and our Rain Barrel Season, is right around the corner. We will be teaming up with the Sierra Club’s Great Lakes Program again this year to promote the use of rain barrels to help reduce Detroit’s combined sewage overflows and storm water pollution. This past weekend we had our first Live Green Fair of the season at Kellogg Arena in Battle Creek.

Last year, we sold 440 rain barrels and hope to better that mark this year. When talking to people about their rain barrels we tell them how quickly they will fill up in a good rain. In talking with Melissa Damaschke of Sierra Club’s Great Lakes Program we decided to attempt quantify the amount of rain water those 440 rain barrels could harvest in a year.

Being that I love researching an issue and spreadsheets, I immediately volunteered. Here is what I found.

The average rainfall in Detroit, MI is 32.89 inches. As reported in many news sources, 2011 was the wettest year in Detroit’s history with 47.7 inches of rainfall. (Climate Change anyone?) The average roof in the U.S. is 2400 square feet. To figure out how many gallons of water you can collect off your roof, just multiply the square footage of roof space by 0.6 gallons per square foot per inch of rain.

Plugging in this formula to the average yearly rainfall we get (2400 sq ft x .06) x 32.89 or 47,361.6 feet of space per house. Multiply this by our 440 rain barrels and in an average year we could help keep 20,839,104 gallons of water out of the storm sewers. Substituting the actual rainfall from 2011 of 47.7 inches and you get a total of 30,222,720 gallons of water saved.

Obviously, this example is based on every rain barrel we sold collecting every drop of rain from every home. In the real world, most people only hook the rain barrel up to one downspout. But even if only 1/4 of the rainwater was collected, that is over 7.5 million gallons of rain that we helped to collect for people to water their gardens, cars, etc. That is over 7.5 million gallons of rain water that did not make it’s way into the Detroit combined sewer system, did not help push raw sewage into the Detroit River and did not help cause one of the worst algae blooms in Lake Erie’s history.

It really is amazing how much good you can do with a simple thing like one of our Terra Cotta Rain Barrels.