What Is a Rain Barrel and How Do I Use One?

The short answer: a rain barrel is a container positioned under or beside a downspout that captures roof runoff, and it is used to water gardens, containers, and lawns during dry spells instead of drawing from the tap. A typical residential barrel holds 50 to 60 gallons, and every full barrel is water that does not race into the storm drain.

Rain barrels are the simplest step in a whole chain of stormwater smarts that includes rain gardens and permeable paving, and they suit both the environmental goal and the practical one, cheaper summer watering in a climate that swings from deluge to drought.

Size the barrel system to the roof section, not the garden: a single downspout on a modest roof section can fill a barrel with one good storm, and a second barrel daisy-chained to the first adds capacity without new plumbing. Count your downspouts and your watering days, and two barrels on the busiest corner often beat one barrel in the middle of nowhere.

The parts

A barrel (often a food-grade former liquid container or a commercially made unit) fits a diverter on the downspout, a screened inlet to keep out leaves and mosquitoes, a spigot near the bottom, and an overflow outlet near the top that routes excess water safely away when the barrel is full.

The setup

Level the barrel on a sturdy base (a full barrel is heavy), connect the diverter so water flows in only when barrels are full, and point the overflow toward a bed, rain garden, or lawn rather than the foundation.

The use

Connect a hose to the spigot, or fill watering cans, for containers, beds, and vegetable gardens. Rainwater is soft and low in minerals, which plants and soil appreciate.

Make the harvest convenient: a barrel on a sturdy base about 18 to 24 inches tall gives gravity enough to fill a watering can, and a short hose with a shutoff nozzle reaches the nearest beds. The barrel you can reach without a step stool is the barrel you will use, and the used barrel is the one that pays.

Rain barrel rules vary by municipality: many Pennsylvania townships welcome them, some restrict placement or require screened outlets, and Philadelphia's stormwater programs actively encourage capturing roof runoff, so check local guidance. Keep the barrel covered and screened so mosquitoes cannot breed, and keep it for plants rather than drinking water, since roof runoff carries debris and bird droppings.

Winter is non-negotiable: drain the barrel, disconnect and open the valve, and store it or flip it before freezing weather, because expanding ice will crack the barrel and the diverter. Reconnect in spring for the season's first storms.

Keep the water clean enough for plants: screen the inlet, flush the first downpour away if you can with a simple diverter that skips roof crud, and empty standing barrels that sit untended between storms to reset them. Rainwater chemistry is gentle on plants, and a little maintenance keeps it that way.

Think about the barrel's seasonality in the design: a barrel that drains through a hose to a distant bed is more useful than one that must be carried to, and a barrel plumbed to a drip line waters the garden on its own in dry weeks. Position the overflow to feed a rain garden or swale so the system handles the storms the barrel cannot hold, and the roof becomes the garden's own irrigation network. That full version, barrel, diverter, drip line, and overflow bed, is the setup that turns a purchase into a system.

A rain barrel pays for itself fastest for gardeners and container growers with hose-length access to the barrel, since it supplies the biggest water bills of summer. For lawn-only water users, a barrel refills after each storm but empties fast on a hot week; a second barrel, or a larger cistern, extends coverage for serious gardens. Add a rain garden or swale at the overflow and the system handles stormwater even in the heaviest Pennsylvania downpours, which is the full version of the idea.

Whatever the setup, position matters: put the barrel where you will actually carry a watering can, because the most technically perfect rain barrel that sits out of reach will sit unused.

Check your township's incentive programs while you shop: Philadelphia and several surrounding communities have supported stormwater capture with rebates or recognition, and some townships simply fast-track the permit when a rain barrel is part of the plan. A five-minute call can turn a small purchase into a small credit.