Rain Barrel Facts
What can I use the rainwater for?
Rainwater by nature is a soft water, void of harsh chemicals or pollutants, usually hitting the soil in its purest form. Rainwater is the most precious source of freshwater on earth, and the most readily available, as only 3/10 of 1% of all the worlds water supply is available in the forms of freshwater reserves such as streams, rivers and lakes. Rain is perfect for indoor and outdoor plants.
How much can I collect?
The amount of rainwater you can collect depends on three factors: The amount of rainfall in a given downpour, the size of your catchment area and the maximum capacity of your storage device (in this case I assume a rain barrel).
Rainfall: This is usually calculated in inches with a rain gauge, or can be predicted by consulting historical records in an almanac or local weather stations and other meteorological and climatic sources.
How often does rain fall where you live and how much tends to fall in what given parts of the year, exactly?
Catchment Area: Looking at a birds eye view of your roof (from directly above), what is the total geometrical area of space available for rain to fall on? That is the total amount of area that will actually catch and redirect water to be harvested (think in two dimensions only, like looking at a bullseye target).
Rainfall in inches, times the catchment area in square feet should render the amount of gallons that have fallen on your roof. The standard calculation is for every single inch of rainfall, on 1,000 square feet of catchment area; 600 gallons of rainwater are thus available.
1 in. (of rainfall) * 1,000 sq.ft. (of catchment area) = 600 gal. (of collectable rainwater)
Maximum Capacity: You should choose a maximum capacity for your rain barrel that is small enough to move around, maintenance and clean and yet meets your rainwater needs throughout your dry spells. The longer the dry spell, the more rain barrels you may need to link up between overflow valves. Do this by calculating how much rainwater you use during those dry spells (gpm or gallons per minute), and knowing which is the harshest (gpm * minutes used * total days of harshest dry period = maximum need), prepare to meet your needs for that one driest moment of the year, and you will be self-reliant all year!