How to Build a Rain Barrel: Parts, Assembly, and Overflow
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To learn how to build a rain barrel, start with a container that catches runoff from a roof downspout and stores it for watering plants. Building one is a modest project: a food-grade barrel, a few PVC fittings, a brass spigot, and a bit of drilling. The steps below follow two university extension guides, one from Penn State Extension that walks through a kit-based build and one from the University of Nebraska-Lincoln that describes a barrel assembled from parts. Where the two differ, the difference is noted.
Quick answer
- Every rain barrel needs a cover, an inlet where rainwater enters, an outlet near the bottom, and an overflow near the top.
- Place the barrel within about three feet of a downspout, on a level, firm base such as concrete blocks or pavers.
- Penn State advises setting the spigot about ten inches up from the bottom. Nebraska places the outlet approximately 2 to 4 inches from the bottom.
- The overflow must be at least 1½ inches and must carry water at least 10 feet from the building foundation.
What every rain barrel needs
The Nebraska guide, How to Make a Rain Barrel (EC2001), lists four required parts regardless of design: a cover, an inlet, an outlet, and an overflow. The cover keeps out mosquitoes, tree leaves, debris, pets, and wildlife. The guide notes that covers can be solid or screened. The inlet can be as simple as a hole cut in the top of the barrel with screen caulked over it, or a downspout extension elbow that fits snugly into a hole in the top. Whatever inlet is used, the guide says it should not allow mosquitoes to enter the barrel, which is why screening or a snug fit matters.
The outlet is usually a spigot or hose bibb in the side of the barrel near the bottom. The overflow is needed because most rain barrels cannot hold all the runoff from even a moderate storm. Nebraska describes the overflow as a PVC elbow set into the side of the barrel near the top, with a PVC pipe or flexible hose attached to carry the excess water away.
Choosing the barrel and fittings
For background on why runoff matters, see how rainwater runoff erodes soil. Nebraska says rain barrels are typically 50 to 100 gallon containers, and that a plastic barrel is relatively easy to work with and inexpensive. The guide recommends a food-grade barrel, or one that did not hold toxic materials, and cites 55 gallons as a common size. Barrels with removable lids are easier to clean, but a closed-top barrel also works. The guide notes that a dark-colored barrel admits less light, which helps reduce algae growth, and that light-colored or translucent barrels can be painted to admit less light.
The Nebraska parts list for a simple barrel includes a PVC drain/waste/vent (DWV) adapter, screen to fit over it, a hose clamp, a ½-inch brass spigot, a PVC trap adapter of at least 1½ inches, a 90-degree PVC street elbow the same size as the trap adapter, a second 90-degree elbow, and PVC pipe of the same size. The guide advises testing that the PVC pieces fit together before buying them all.
Penn State sells a kit rather than listing individual parts. Its kit includes a spigot, a downspout adapter, a flexible connector hose, three hole saws, a drill bit, two rubber seals, and two screws. Penn State lists the extra supplies a builder needs as safety glasses, a drill, a measuring tape, a pencil or marker, a level, a screwdriver, and scissors.
Tools and materials
For the Nebraska design, the guide lists an electric drill with a 15/16-inch spade bit and a hole saw matching the threaded end of the trap adapter, a jigsaw, a hacksaw, a pocket knife, a flat-blade slot screwdriver, a tape measure, a marking pen, a carpenter’s level, and optional thread seal tape or outdoor caulk. It also lists concrete blocks or pavers for the base, and safety glasses, ear plugs, and heavy-duty gloves.
Step 1: Pick the location and base
Penn State says to choose a downspout that is easy to reach and to keep the barrel within three feet of it. The ground should be level and firm. Penn State recommends using sand or gravel to level the area and setting the barrel on a cinder block or bricks, because elevation increases water pressure out of the spigot. Nebraska agrees that the base should be flat, level, and stable, since a 55-gallon barrel of water weighs over 400 pounds. Nebraska also notes that elevating the barrel gives clearance for a hose or a watering can under the outlet and lets water flow out a little faster.
Nebraska recommends deciding on the location before buying parts. It says the site should be fairly level and have good drainage away from the building foundation for the overflow. The barrel should also be close to the plants it will water, or convenient to a door if the water is for houseplants.
Step 2: Install the spigot
Penn State measures up ten inches from the bottom of the barrel on the front face, marks the spot, and drills with the small 1¼-inch hole saw. It says to insert the threaded rubber seal while pinching it, then thread the spigot into the seal until it is firmly in place with the spigot pointing down.
Nebraska drills a 15/16-inch hole in the side of the barrel about 2 to 4 inches from the bottom for the outlet spigot. The guide explains that a low outlet leaves less water stranded in the barrel after emptying. When screwing in the brass spigot, Nebraska says to keep it as straight as possible, and if it will not fit, to ream the hole with a pocket knife until it is slightly larger. The spigot should fit tightly to prevent leaks.
Step 3: Install the inlet and downspout connection
Penn State drills a 1½-inch hole for the inlet fitting on the opposite side of the barrel, measured down three inches from the top. It then marks the diverter hole on the downspout by laying a level across the top of the barrel toward the downspout. The large 2⅛-inch hole saw cuts the downspout hole. The diverter is squeezed into the hole with its cup facing up, and two screws hold it in place. A hose connects the diverter to the barrel’s inlet, and the hose can be cut to shorten it.
Nebraska takes a different approach for a barrel without a diverter. It describes cutting the downspout to length so the remaining section rests on or hangs slightly above the DWV adapter and empties into the barrel. The guide suggests saving the cut piece of downspout to reinstall in the fall when the barrel is removed for winter storage. For the inlet hole itself, Nebraska advises tracing around the smaller end of the DWV adapter, keeping the hole away from the rim because the barrel is thicker there, and cutting it out with a jigsaw.
Step 4: Build and place the overflow
Nebraska drills the overflow hole near the top of the barrel, after feeling inside the barrel for a thicker section and drilling below it. The guide says the barrel has a curved surface, so some parts may not sit flush with it, which is usually not a problem. The trap adapter goes through the overflow hole from outside, and a ring is screwed on from inside to hold it. The street elbow attaches to face downward.
The overflow pipe is cut to length by marking the vertical pipe at the level of the street elbow, then extra PVC pipe carries water at least 10 feet from the building foundation. Nebraska says the pipe should slope slightly to drain water in the desired direction and that the overflow can go to a rain garden, landscape bed, lawn, or another pervious surface. The guide also warns that a regular garden hose spigot used as an overflow will not be large enough. The smallest overflow that should be used is 1½ inches. If the overflow is too small, water can flow out of the top of the barrel and potentially damage the building foundation.
Nebraska also describes a flexible overflow option. It uses a 2-inch flat discharge hose of about 12 to 14 feet that fits over a 1½-inch PVC street elbow and is secured with a hose clamp. The guide says the hose must still be positioned to carry overflow away from the foundation.
Step 5: Check after the first rain
After the first rainfall, Nebraska recommends checking that everything works and cleaning the inlet and any filters or screens on a regular basis. Penn State recommends inspecting the barrel regularly for leaks, clearing debris from the downspouts and gutters or from inside the barrel, and confirming that the spigot and inlet work properly.
Maintenance and winter storage
Penn State says it is critical to disconnect and empty the barrel before winter so that no water can freeze and crack it, and to reconnect it in spring. Nebraska makes the same point in its guide, noting that the removed downspout piece can be reinstalled in fall when the barrel is stored. Neither guide gives a specific freezing temperature, so the timing will depend on the local climate. Nebraska’s point that the overflow should drain to a pervious surface is about soaking water into the soil rather than letting it run off, so the same runoff question applies to bare soil, as covered in how rain splash erodes bare garden soil.
What we could not verify
What the sources do not say
The two guides do not agree on the spigot height. Penn State uses about ten inches from the bottom and says the raised height increases pressure. Nebraska uses 2 to 4 inches and says a low outlet leaves less water behind. Both positions come from the sources, and the choice is a trade-off the builder has to make.
Neither source gives a volume or flow rate for how fast a barrel will drain, and neither gives a total yield figure for a given roof area. The Nebraska guide describes rain barrels as a way to reduce runoff and says that the amount collected in one barrel is small. It does not quantify the effect on a particular property.
The Penn State page describes a kit and does not give a full list of dimensions or drill sizes beyond the hole saws in its steps. Builders working from a different barrel shape should check the fittings against the barrel before drilling.
How we chose these sources
The two sources were chosen because each is a university extension publication that covers a complete build. Penn State Extension covers a kit-based install with photos and step numbers. The University of Nebraska-Lincoln covers a from-parts build with cutting and drilling instructions and overflow options. The two guides are independent of each other. Both were opened on 2026-10-30 and their full text was read.
Frequently asked questions
Do you need a cover on a rain barrel?
Nebraska says a cover is one of the required parts of any rain barrel. It says covers keep out mosquitoes, leaves, debris, pets, and wildlife, and that covers can be solid or screened.
How high should the spigot be on a rain barrel?
Penn State says to measure up about ten inches from the bottom and says that elevating the barrel increases the pressure at the spigot. Nebraska places the outlet about 2 to 4 inches from the bottom so that less water stays in the barrel.
How big should the overflow be?
Nebraska says the smallest overflow that should be used is 1½ inches. It warns against using another spigot with a garden hose as the overflow because the hose is too small.
How far should the overflow water go from the house?
Nebraska says to direct the overflow at least 10 feet from the building foundation, to a location where the water can safely soak into the soil, such as a rain garden or lawn.
What should you do with a rain barrel in winter?
Penn State says it is critical to disconnect and empty the barrel before winter so that the water cannot freeze and crack it, and to reconnect it in the spring.
Sources
- Penn State Extension, “Rain Barrel Construction Guide,” https://extension.psu.edu/rain-barrel-construction-guide (opened 2026-10-30).
- University of Nebraska-Lincoln Extension, EC2001, “Stormwater Management: How to Make a Rain Barrel,” https://extensionpubs.unl.edu/publication/ec2001/2014/pdf/view/ec2001-2014.pdf (opened 2026-10-30).
