Growing up Grandma had a large flat rock off to the side of her front door where a small rain barrel sat. We were required to stand on that rock and take a scoop of rain water to wash our feet off before coming into the house. The water was always cold and clean. Her barrel had a lid on it, which she would crack whenever it rained to catch what came off the roof. I tell people all the time, Grandma was the original "green" queen. Nothing escaped her when it came to recycling or re-purposing things. But those are other stories waiting to be told.
We have 3 barrels and from the looks of the formula below, we are missing out on capturing a whole lot more!
How much rain you can catch:
Rain caught (gallons) = (inches of rain) x (0.6) x (portion of building footprint in ft2)
For example, if your home's footprint is 1,400 ft2, and you want to know the amount of water that comes from a ¼ inch of rainfall the equation would look like this:
Rain caught (gallons) = (0.25) x (0. 6) x (1,400) = 210 gallons.
However, remember that storage is limited to the capacity of your system. If your rain barrel holds 50 gallons, then 160 gallons will be lost.