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Connecting two rain barrels lets them share stored water and gives you more capacity without adding a larger tank. The simplest setup is usually to connect the barrels near the bottom so water can move between them and both barrels rise and fall together.
Another option is an overflow connection near the top. That is easier to install in some systems, but the second barrel does not begin filling until the first barrel is nearly full.
For a modular connection, rain barrel linking kits can provide matched bulkheads, hose, and seals for expanding storage.
Two Common Ways to Connect Rain Barrels
You can connect two rain barrels in one of two basic ways:
| Connection method | How it works | Best for |
|---|---|---|
| Bottom connection | Water flows between both barrels as they fill and empty | Using both barrels as one storage system |
| Top overflow connection | The first barrel fills before water enters the second | Simple expansion of an existing barrel |
For most permanent two-barrel systems, a bottom connection gives more balanced storage and easier water use.
How a Bottom Connection Works
With a bottom connection, a hose or pipe joins the barrels close to their bases. Because the water is connected, gravity tries to keep the water level the same in both barrels.
If rain enters only the first barrel, water flows through the connecting line into the second barrel.
When you draw water from one barrel, water from the other barrel can also move through the connection.
This setup works best when both barrels:
- Sit at about the same height
- Have connections at about the same level
- Use a connecting line large enough to move water freely
- Have a stable, level base
A narrow connection may transfer water slowly during heavy rain. The first barrel could temporarily rise faster than the second.
What You Need
The exact fittings depend on your barrels, but a typical connection uses:
- Two rain barrels
- Two tank fittings or bulkhead fittings
- Flexible hose or rigid pipe
- Matching adapters or unions
- Hose clamps if required by the hose system
- Valves if you want to isolate the barrels
- Suitable washers or seals
- An overflow line
- Inlet screening to keep insects and debris out
A bulkhead fitting is a fitting that passes through the wall of a container and creates a sealed connection for a pipe or hose.
Choose fittings that are designed for the wall thickness and shape of your barrels. Do not assume fittings intended for one barrel will seal correctly on another.
How to Connect Two Rain Barrels at the Bottom
1. Choose the barrel locations
Place the barrels next to each other on a solid, level base.
Remember that water is heavy. A full barrel can weigh hundreds of pounds. The base must support the barrels without sinking, leaning, or shifting.
Do not place large water containers on decks or elevated structures unless you know the structure can safely support the load.
2. Decide where the connecting ports will go
Choose locations low on each barrel but high enough that you can install and service the fittings.
The two ports should be at roughly the same height.
Avoid drilling through:
- Molded seams
- Strong ribs
- Curved areas that prevent the fitting from sitting flat
- Areas too close to the bottom for the fitting hardware
Check the requirements of your fitting before drilling.
3. Empty the barrels
Do not drill into a full or partially full barrel.
Emptying the barrels also makes them easier to position and reduces the chance of movement while you work.
4. Mark the holes carefully
Measure from the base or another fixed reference point so both connection holes are at approximately the same height.
Check the measurements before cutting.
The hole must match the fitting manufacturer's required hole size. A hole that is too large may be difficult or impossible to seal reliably.
5. Install the tank fittings
Install a bulkhead fitting or another fitting designed for water tanks in each barrel.
Follow the fitting manufacturer's instructions for:
- Hole diameter
- Gasket placement
- Nut orientation
- Tightening
Do not automatically add sealant to every gasketed fitting. Some fittings are designed to seal with their gasket alone.
Overtightening can deform a plastic barrel or gasket and cause leaks.
6. Connect the barrels
Join the two fittings with a flexible hose or pipe.
Flexible hose is useful when the barrels may move slightly because of temperature changes or settling. Rigid pipe can provide a neat installation, but the barrels and fittings need to stay properly aligned.
Avoid putting the weight of long unsupported pipe on the barrel wall.
A union or other removable connection can make future barrel cleaning much easier.
7. Add isolation valves if useful
A valve on each barrel connection is optional, but it can make maintenance easier.
For example, you could close the valves and remove one barrel for cleaning while leaving the other in place.
Make sure any valve does not restrict the connection excessively.
8. Test the connection
Add a small amount of water before filling the entire system.
Look closely around:
- Bulkhead fittings
- Gaskets
- Hose connections
- Valves
- Threaded adapters
If everything stays dry, gradually raise the water level and check again.
A connection that does not leak with one inch of water above it may still leak when the barrel is full and pressure at the fitting is higher.
How to Connect Two Rain Barrels With an Overflow Hose
An overflow connection works differently.
Instead of connecting the barrels near their bottoms, install a connection high on the first barrel and route it into the second.
During rain:
- Water enters the first barrel.
- The first barrel fills.
- Water reaches the upper connection.
- Excess water flows into the second barrel.
- The second barrel begins filling.
This setup can be easier when you are adding a second barrel to an existing system.
The tradeoff is that the barrels do not act as one reservoir. If your faucet is on the first barrel, water stored below the upper connection in the second barrel will not automatically flow back into the first.
You may need a separate outlet or another way to use water from the second barrel.
Should You Use Hose or PVC Pipe?
Either can work.
Flexible hose
Flexible hose is often easier for a two-barrel system because it tolerates small alignment differences.
It can also make barrel removal easier.
Make sure the hose:
- Fits the adapters correctly
- Is suitable for outdoor water use
- Does not kink between barrels
- Is protected from damage
PVC or other rigid pipe
Rigid pipe can provide a firm, tidy connection.
It works best when the barrels sit securely and the fittings align well. Include a removable fitting such as a union if you expect to separate the barrels for cleaning.
Do not force misaligned rigid pipe into place. That can put stress on the barrel fittings and increase the chance of leaks.
How Large Should the Connecting Pipe Be?
There is no single correct size for every system.
The connection needs enough capacity to move water from the receiving barrel into the second barrel without the first barrel filling much faster than water can transfer.
Regarding considerations before connecting rain barrels at top or bottom, assess safe ventilation and overflow routing for stored water.
The required size depends partly on:
- Roof area draining to the system
- Rain intensity
- Downspout flow
- Connection length
- Fittings and bends
- Height of the connecting ports
A very small hose may work during light rain but become a bottleneck during a heavy storm.
Regardless of the interconnection size, provide a properly routed overflow. Do not depend on the barrel-to-barrel connection as the system's only protection against overflowing.
Where Should the Overflow Go?
The final barrel needs a safe overflow path.
Route overflow water away from places where it could cause problems, including:
- Building foundations
- Crawl spaces
- Basement walls
- Walkways
- Neighboring property
- Areas prone to erosion
The overflow must be able to handle incoming water after the storage system is full.
Keep overflow openings screened where needed to limit insect and pest entry.
Do Both Barrels Need to Be the Same Size?
Not necessarily.
Two different-size barrels can share water through a bottom connection as long as their connection heights and operating water levels work together.
However, barrels with very different shapes can make fitting placement more difficult.
The important point is that neither barrel should be filled above its safe operating level simply because the other barrel is taller.
Your overflow should control the maximum water level.
Can One Downspout Fill Both Barrels?
Yes.
You normally need only one rainwater inlet when two barrels are connected near the bottom. The downspout can feed the first barrel, and water will move into the second through the connecting line.
This simplifies the roof connection.
Keep leaves and larger debris out of the barrels with suitable gutter maintenance and inlet screening. A first-flush device may also be used in some systems.
A first flush device diverts some of the initial roof runoff, which often carries more dirt and debris from the roof.
It does not make the remaining rainwater safe to drink.
Keep the Barrels at the Same Height
For a bottom-connected system, the barrels should normally sit on the same level base.
If one barrel is substantially higher than the other, the system will behave differently because water seeks the same level across connected containers.
The lower barrel could reach its maximum level before the higher barrel appears full.
Level the base rather than trying to correct a large height difference with the plumbing.
Leave Room for Cleaning
Do not build the connection so tightly that the barrels become impossible to service.
Rain barrels collect sediment over time. Screens, hoses, fittings, and barrel interiors may all require cleaning.
Useful features include:
- Shutoff valves
- Pipe unions
- Removable hoses
- Accessible cleanout openings
- Enough space to reach fittings
Good service access can save much more work later.
Protect the System in Freezing Weather
Water trapped in a barrel, valve, fitting, or connecting pipe can freeze and expand.
If freezing temperatures occur in your area, follow a winter setup appropriate for your barrels and plumbing. This may involve draining and disconnecting parts of the system before sustained freezing weather.
Do not assume a flexible hose or plastic barrel is freeze-proof.
Follow the barrel and fitting manufacturer's cold-weather guidance.
Common Problems With Two-Barrel Systems
The second barrel fills very slowly
The connection may be too small, kinked, blocked, or partially closed.
Check the connecting line and fittings for restrictions.
One barrel fills but the other stays almost empty
Check whether the connecting valves are open and whether the pipe is blocked.
Also confirm that a bottom connection actually contains water. If the connection is above the water level, water cannot transfer through it.
A fitting leaks
Empty the barrel below the fitting before working on it.
Check gasket position, fitting alignment, hole size, and tightening instructions. Simply tightening the fitting harder can sometimes make the leak worse.
The first barrel overflows during heavy rain
The transfer connection may not move water as quickly as rain enters the barrel.
Make sure the system has a separate overflow capable of safely carrying excess water away.
Water does not drain evenly
Check that both barrels are sitting level and that the connecting line is not kinked, blocked, or positioned in a way that traps water.
Do Not Treat Connected Rain Barrels as Drinking-Water Storage by Default
Roof-collected rainwater can contain microorganisms, animal waste, roofing contaminants, dirt, and other pollutants.
Connecting two barrels does not change the water quality.
For garden irrigation and other non-potable uses, appropriate screening, storage, and maintenance may be sufficient depending on the intended use and local requirements.
Potable means water suitable for drinking. Non-potable means water that is not intended for drinking.
If you plan to use collected rainwater for drinking, cooking, or other potable household uses, treat it as a whole-system water-safety project. Suitable collection materials, prefiltration, treatment, current laboratory testing, regular maintenance, and applicable local requirements all matter. A single filter or treatment device should not be assumed to make roof runoff safe to drink.
Frequently Asked Questions
Can I connect two rain barrels with a garden hose?
Yes, if both barrels have compatible fittings and the hose provides enough flow for the system. A small garden hose can transfer water between barrels, but it may move water too slowly during heavy rain. Keep a separate overflow on the system.
Should rain barrels be connected at the top or bottom?
A bottom connection is usually better when you want both barrels to behave like one storage system. A top connection works well when you simply want excess water from the first barrel to fill a second barrel.
Will two connected rain barrels fill at the same rate?
With a sufficiently large bottom connection, they should move toward the same water level. They may not rise at exactly the same rate during heavy rain if the connecting line restricts flow.
Do I need a faucet on both rain barrels?
Not necessarily. With a bottom-connected system, a faucet on one barrel can often draw water from both because water transfers between them. Separate outlets may still be useful for maintenance or different watering areas.
Can I connect more than two rain barrels?
Yes. The same basic principle can be used for several barrels. As the system becomes larger, connection size, overflow capacity, base stability, pipe support, and isolation for maintenance become more important.
Does the second rain barrel need an overflow?
The system needs a safe final overflow. In a two-barrel arrangement, this is commonly installed on the final barrel or at another point that controls the maximum water level of the entire system.
Can the barrels sit at different heights?
A small difference may occur in real installations, but bottom-connected barrels work best on a level base. Significant height differences can cause one barrel to reach its maximum water level before the other.
