Rain Barrels

Rain barrels are an excellent way to make use of the free rain water that falls on your roof, reducing your water costs and water footprint. Rain barrels come in many different forms, but the most common (and most efficient) type harvests water from your roof via your downspouts. These barrels can harvest around 600 gallons per inch of rain that falls on a 1000 sq. ft. area.
This statistic has a caveat, however. Since most roofs have many different slopes (and many different downspouts), you will need several rain barrels to utilize the complete surface area of your roof. Thus, if your entire roof is 1000 sq. ft. but has two slopes, you would need two rain barrels – one for each slope – to use the entirety of your roof.
Roof-collection barrels also have a few other caveats. They will collect whatever chemicals that may be on your shingles in order to resist rot and fungal growth. Rain barrels connected to metal roofs may also yield unpotable water – rainwater can leach some metal and metal oxides from the roof which then run off into the rain barrel. Due to this, any water collected from roof-collection barrels should only be used for watering inedible plants or in graywater systems. Most rain barrel water, unless filtered, is unsuitable for drinking or plants intended for consumption.
Rain barrels have a wide range of sophistication. You can purchase rain barrels designed specifically for rain water collection at many hardware stores (see links below), but you can also make your own rain barrel out of a repurposed barrel or even a plastic garbage can. Links to both store-bought and DIY rain barrels are listed below: