Rain Barrel Setup: Downspout Diverters, Overflow, and Using Collected Water

Choosing and Placing the Barrel

Buy a food-grade barrel (55 or 65 gallons) or a purpose-built rain barrel with an integrated screen, spigot, and overflow port. Food-grade drums from soft drink bottlers or food processing plants work well and cost less than retail rain barrels.

Place the barrel directly under a downspout on a level, stable surface. Elevate the barrel 12 to 24 inches on cinder blocks or a dedicated platform — gravity-fed pressure from a barrel sitting on the ground is too weak to push water through a hose. Every foot of elevation adds about 0.43 PSI of pressure.

A full 55-gallon barrel weighs about 460 pounds. Whatever you place it on must support that weight without sinking into the ground. A paver pad or compacted gravel works. Soft soil does not.

Check local regulations. Some municipalities regulate rainwater collection. Most allow it for garden irrigation. A few states (primarily in the arid West) have complex water rights laws that historically restricted collection, though most have been updated to allow residential barrels.

Downspout Diverter Installation

A downspout diverter (also called a rainwater diverter or first-flush diverter) connects the barrel to your existing gutter downspout. The simplest version cuts the downspout and redirects flow into the barrel. A better version includes an automatic bypass that routes water back to the downspout once the barrel is full.

Cut the downspout at the height where the barrel inlet is located. Attach the diverter fitting. Most diverters connect with sheet metal screws and come with adapters for standard 2x3-inch and 3x4-inch rectangular downspouts, as well as 3-inch and 4-inch round downspouts.

Install a fine mesh screen over the barrel inlet to keep leaves, debris, and mosquitoes out. Many barrels come with a built-in screen. If yours does not, a piece of aluminum window screen over the opening, secured with a hose clamp or bungee, works.

Overflow Management

An overflow port near the top of the barrel routes excess water away from the foundation when the barrel is full. This is the single most important detail people skip. Without overflow routing, water pours over the top of the barrel and pools against the house — worse than not having a barrel at all.

Connect a garden hose or PVC pipe to the overflow port and direct it to a garden bed, a rain garden, a dry well, or back to the downspout below the diverter cutpoint. The overflow discharge should be at least 4 feet from the foundation.

You can chain multiple barrels together with a hose connecting the overflow of one barrel to the inlet of the next. This increases storage capacity and delays overflow. Three 55-gallon barrels provide 165 gallons of storage.

Using Collected Rainwater

Rain barrel water is safe for watering lawns, gardens, flower beds, and non-edible landscaping. For vegetable gardens, apply the water to the soil around the base of plants — not to the leaves or edible parts — to minimize any risk from roof runoff contaminants.

Do not use rain barrel water for drinking, cooking, bathing, or filling pools and hot tubs. Roof runoff can contain bird droppings, shingle compounds, pollen, and other contaminants.

Use a watering can or a soaker hose connected to the spigot. The gravity-fed pressure from a barrel is low — about 1 to 2 PSI. This is not enough pressure for a sprinkler. A soaker hose works because it is designed for low-pressure drip delivery.

Drain the barrel before the first hard freeze in cold climates. Ice expansion can crack the barrel. Store the barrel upside down or inside over winter.

Mosquito Prevention

Standing water breeds mosquitoes. A rain barrel with an open top or a loose screen becomes a mosquito nursery within days.

Keep all openings screened — inlet, overflow port, and spigot (if the spigot is left open with no hose attached). Fine mesh window screen with openings smaller than 1/16 inch keeps mosquitoes out.

If mosquito larvae appear in the water, add a mosquito dunk (Bti — a biological larvicide) to the barrel. One dunk treats 100 square feet of water surface and lasts 30 days. Bti is non-toxic to humans, pets, fish, and plants.

Use the water regularly. A barrel that sits full for weeks without being drawn down provides ideal mosquito breeding conditions. Regular use and refilling disrupts the breeding cycle.

Frequently Asked Questions