What Is a Rain Barrel and How Does It Work?

A rain barrel is a covered container, typically 50 to 60 gallons, connected to a downspout so it fills with roof runoff instead of sending it all to the storm drain. A diverter on the downspout directs water into the barrel; when the barrel is full, the diverter lets the overflow continue down the downspout as normal. A screened inlet keeps out leaves and mosquitoes, and a spigot near the bottom lets gravity feed a watering can or a short hose.

Every inch of rain on a modest roof sheds far more water than a barrel holds, which is the point: the barrel captures the first flush for your garden, and the rest goes where it always did. Using that captured water for plants means the municipal water you would have sprinkled is still in your pipes.

Neighborhood stormwater programs are worth a second look even for homeowners who never water a garden: some municipalities tie rain barrel purchases to stormwater fee credits, and a few subsidize the barrel heavily when you attend their workshop. The barrel then pays for itself twice, once in reduced watering and once in reduced fees. Ask your township's public works or stormwater office what programs exist, because the answer varies block by block across the Philadelphia region and you may be eligible without knowing it.

Rain barrel water is perfect for outdoor plants and flowers, and it is often better for them than treated tap water. Rain carries none of the chlorine or fluoride found in municipal supplies, and its slightly acidic nature suits most garden plants. Use it for flower beds, container plants, vegetable gardens, shrubs, and lawns. It is not drinking water, and it should not be used for household plumbing.

Because you control it, barrel water is easy to time: fill cans in the morning after a storm, and water beds during the cool hours when evaporation is low. In a dry Pennsylvania August, a barrel or two can cover a surprising share of a garden's needs.

Good setup means a stable base, a sealed top, and a working overflow. Place the barrel on a sturdy, level stand a foot or two off the ground so a watering can fits under the spigot and the gravity flow is strong. Keep the lid and screen tight to block mosquitoes, and make sure the overflow is directed away from the foundation. Many townships in the region sell rain barrels at discounted workshops or provide instructions with their stormwater programs, which is a great way to start.

Before winter, disconnect the barrel, drain it completely, and store it upside down or inside. A full barrel left outside freezes, expands, and cracks. Disconnecting the downspout section also lets roof melt and ice drain normally through the winter.

Rain barrels are a stormwater tool as much as a water-saving tool. In developed Philadelphia suburbs, summer storms send runoff, and everything it carries, straight into storm sewers and creeks. Every barrel slows a little of that flow and lets the water soak into your garden instead, which reduces local flooding pressure and keeps the first flush of roof debris out of the system.

Some municipalities offer rebates or discounted barrels through stormwater programs, so ask your township or county conservation district before you buy at retail.

Rain barrels capture a surprising amount of water for their size, and the math helps you size your setup. The rule of thumb used by extension offices is that every inch of rain on a roof sheds roughly half a gallon for each square foot of that roof footprint. A modest suburban roof section of a few hundred square feet therefore produces far more than any barrel holds: a 600-square-foot roof area sheds somewhere around 300 gallons in an inch of rain. That is the reality behind the design, and it explains why barrels are sized to capture the amount that makes watering convenient rather than the full storm.

For most gardens, the practical layout is one barrel on the downspout nearest the flower beds, with a diverter and a linking kit so a second barrel fills after the first. If you water heavily, position the barrels for easy filling of watering cans or run a short soaker hose from the spigot down a bed. The barrel refills with every storm, so even a pair of 60-gallon barrels can carry a surprising share of a season's watering during the wetter stretches, and during a dry spell you supplement from the tap only as the barrels empty.

Track your own numbers for a season: count how many times the barrels empty into the garden, and you will know exactly what another barrel or a taller stand is worth to your water bill.