Rain barrels capture roof runoff for garden irrigation, livestock watering, and other non-potable uses. A typical DIY system consists of a food-grade barrel fitted with an inlet strainer, an overflow port, a spigot, and a stand to provide gravity pressure.
Food-grade plastic barrels of 55 gallons (208 liters) are the standard vessel, sourced from soda syrup, olive oil, or juice concentrate suppliers. Blue or white barrels are preferred for their opacity, which prevents algae growth. Steel drums can also be used but require interior rust-proofing. Barrels that previously contained chemicals other than food should never be reused for water collection.
The inlet is cut into the barrel top or side and fitted with a mesh screen to exclude debris and mosquitoes. A standard downspout diverter connects the gutter to the barrel inlet, directing water into the barrel and routing overflow back to the downspout when the barrel is full. An overflow port near the top of the barrel is plumbed to a second barrel or to a drainage area. A brass or nylon spigot at the base provides water access.
The barrel is elevated 30 to 60 centimeters (12 to 24 inches) on a stand of concrete blocks, landscape timbers, or dimensional lumber. Each 30 centimeters (12 inches) of elevation provides roughly 3 kPa (0.4 PSI) of water pressure at the spigot.
Systems with multiple barrels are linked by near-bottom and near-top connectors using flexible hose or PVC pipe. The first barrel fills and overflows into the next through the upper connector, while the lower connector equalizes water levels. Up to 4 barrels can be linked on a single downspout, providing 220 gallons (830 liters) of storage.