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Joining two rain barrels together is a simple way to increase storage without replacing your existing barrel. The most common method is to connect the barrels near the bottom with a hose or pipe. This lets water move between them until both barrels reach about the same water level.
You can also connect the barrels near the top so the first barrel fills before water spills into the second. That setup is easier to isolate, but it does not balance the water level between the barrels.
The best method depends on how you want the barrels to fill, drain, and connect to your garden line.
Two Main Ways to Connect Rain Barrels
There are two practical layouts:
- Bottom connection: Both barrels fill and drain together.
- Top connection: The first barrel fills, then sends overflow into the second.
Neither method is automatically better. They behave differently.
Bottom Connection
A pipe or hose connects the barrels several inches above their bottoms.
As rain enters one barrel, water moves through the connecting line into the other. Because water seeks the same level, the water surfaces in both barrels gradually become equal.
This setup works well when you want the two barrels to act almost like one larger tank.
For example, two 55-gallon barrels connected at the bottom can provide roughly 110 gallons of gross storage capacity. Actual usable volume will be somewhat lower because outlets, sediment space, overflow height, and barrel shape can leave some water unavailable.
Top Connection
The first barrel receives water from the downspout. A hose or pipe near its upper portion sends excess water to the second barrel.
The first barrel must reach the connecting outlet before much water enters the second barrel.
This arrangement is sometimes called a cascading setup.
It can be useful when:
- You already have an overflow fitting on the first barrel.
- You want the barrels to fill one after another.
- The barrels cannot easily be connected near their bottoms.
- You want fewer low-level fittings that could leak.
The tradeoff is that the barrels do not naturally share water during use.
Which Connection Method Should You Use?
For most side-by-side barrels that will feed the same garden hose or watering system, a bottom balance connection is usually the more convenient setup.
Both barrels contribute stored water, and their water levels stay close together.
A top connection makes more sense when your main goal is simply to capture overflow from one barrel in another.
Here is the difference:
| Setup | How It Fills | How It Drains | Best For |
|---|---|---|---|
| Bottom connection | Both barrels fill together | Both barrels can drain together | Treating two barrels as one storage system |
| Top connection | First barrel fills before second | Barrels may need separate outlets | Simple expansion and overflow capture |
What You Need to Join Two Rain Barrels
The exact fittings depend on the barrels you have, but a typical bottom-connected system needs:
- A water-storage-safe hose or pipe
- Two tank fittings or bulkhead fittings
- Seals or gaskets made for the fittings
- Any required hose adapters
- Shutoff valves if you want to isolate either barrel
- An overflow line
- A stable, level base for both barrels
A bulkhead fitting passes through the wall of a barrel and creates a sealed connection for pipe or hose.
Do not assume fittings with similar-looking sizes will connect correctly. Pipe thread size, hose size, tubing diameter, and actual opening diameter are not always the same measurement.
Check all fitting sizes before drilling the barrels.
Choose the Barrel Location First
Set up the barrels before deciding exactly where to drill.
Both barrels should rest on a firm, level surface that can support their full weight.
Water is heavy. One US gallon weighs about 8.3 pounds. That means a 55-gallon barrel can hold more than 450 pounds of water before you include the weight of the barrel itself.
Two barrels can therefore place close to 1,000 pounds on a small area.
Use a stable base such as properly supported concrete, pavers, or another structure suitable for the expected load. Do not place full barrels on loose soil, unstable blocks, weak decking, or a platform that was not designed for the load.
The barrels should also be close enough that the connection between them does not need a long, awkward hose.
How to Connect Two Rain Barrels at the Bottom
A bottom connection works best when both barrels are at roughly the same elevation.
1. Empty the Barrels
Work on empty barrels whenever possible.
A full barrel is difficult to move, and drilling into a barrel that contains water can quickly become messy.
Clean out any heavy sediment while the barrels are empty.
2. Position the Barrels
Place the barrels where you intend to use them.
Make sure:
- Both are stable.
- Their bottoms are approximately level with each other.
- You have access to the connection points.
- The downspout can reach the inlet.
- The overflow can safely discharge away from foundations and areas that should remain dry.
Do not permanently connect the barrels until you are satisfied with their position.
3. Choose the Connection Height
Place the balance line fairly low if you want access to most of the stored water.
However, putting a fitting at the absolute lowest point is not always necessary.
Leaving some space below the connection can allow sediment to settle without immediately entering the hose or pipe.
You also need enough flat barrel wall around the fitting for the gasket to seal correctly.
Avoid drilling through:
- Molded ribs
- Curved edges
- Seams
- Damaged plastic
- Areas where the fitting cannot sit flat
4. Mark Matching Connection Points
Measure from a common reference point and mark the connection height on both barrels.
The fittings should be at approximately the same elevation once the barrels are sitting on their final base.
Perfect alignment is less important when using flexible hose, but large height differences can affect how much water remains accessible.
5. Drill the Openings
Use the hole size required by your specific bulkhead fitting or tank fitting.
Do not choose a hole saw based only on the fitting's advertised pipe size. The hole through the barrel is often larger than the nominal pipe connection.
Check the fitting manufacturer's required hole diameter.
Drill carefully so you produce a clean opening without cracking the barrel.
Remove plastic shavings before assembling the system.
6. Install the Bulkhead Fittings
Install each fitting according to its instructions.
The gasket normally needs to sit against the correct surface to create the seal. The exact arrangement varies by fitting design, so do not assume that adding extra washers, sealant, or tape will improve the connection.
Overtightening can deform a plastic barrel wall or damage a gasket.
The goal is a secure, evenly compressed seal.
7. Connect the Barrels
Attach the hose or pipe between the two fittings.
Flexible hose can make installation easier because the barrels do not need perfectly aligned fittings.
Keep the connecting line:
- As short as practical
- Free of sharp bends
- Protected from being kicked or pulled
- Large enough for the flow you expect
A very small hose can balance the barrels slowly during heavy rainfall. Water may temporarily rise much higher in the first barrel than in the second.
A larger connection generally allows the levels to equalize faster.
8. Add Isolation Valves if Useful
A valve between each barrel and the balance line is optional, but it can make maintenance easier.
With valves, you may be able to isolate one barrel while cleaning or repairing the other.
Without valves, opening the connection on one barrel may drain water from both barrels.
Any valve you install should remain accessible.
9. Test the Connections
Before relying on the system during a storm, add a modest amount of water.
Check:
- Both bulkhead fittings
- Hose connections
- Threaded joints
- Valves
- The barrel walls around the fittings
Then add more water and check again.
Small leaks sometimes appear only after the water level rises and pressure at the lower fittings increases.
Do not assume a dry fitting after a few minutes will remain leak-free indefinitely. Check the connections again after the system has been filled and used.
How Water Moves Between Bottom-Connected Barrels
The movement does not require a pump.
If the bottoms are connected and both barrels are open to atmospheric pressure, gravity causes the water levels to move toward the same height.
Suppose rainwater enters Barrel A.
Its water level begins to rise. Because Barrel A now has a higher water level than Barrel B, water flows through the connecting hose toward Barrel B.
The levels eventually become similar.
The speed depends partly on:
- Connection diameter
- Hose length
- Bends and restrictions
- Height difference between the water levels
- Blockages or sediment
A balance line should not be confused with the barrel's overflow system. The connecting pipe moves water between barrels. An overflow provides a controlled exit once the storage system is full.
Do Both Barrels Need a Spigot?
Not necessarily.
With a low balance connection, you can often draw water from one barrel and have water from the second barrel flow across to replace it.
That lets you use one main spigot or outlet.
However, the connecting line must be low enough and large enough to transfer water at the rate you are removing it.
Separate outlets may still be useful for:
- Cleaning
- Complete draining
- Isolating a barrel
- Feeding different garden areas
If you install multiple outlets, make sure their positions do not interfere with the balance line.
How to Connect the Barrels at the Top Instead
A top connection is simpler when you want Barrel B to receive only the overflow from Barrel A.
1. Set the Barrels on Stable Bases
The second barrel can sometimes sit at the same height or somewhat lower than the first, depending on the connection layout.
Review practical steps for connecting two rain barrels together to evaluate overflow capacity and ventilation for long-term storage.
Water must be able to move downhill through the transfer hose.
Avoid creating a hose route that rises significantly before reaching the second barrel. A poorly routed line can trap air or reduce gravity flow.
2. Install an Outlet Near the Top of Barrel A
This outlet determines when water begins moving into Barrel B.
It should be below the maximum safe water level of the first barrel.
3. Run the Transfer Line to Barrel B
Connect the first barrel's transfer outlet to a suitable inlet on the second barrel.
Use a line large enough to handle incoming stormwater.
A small transfer hose can become a bottleneck during intense rainfall.
4. Give the Second Barrel Its Own Overflow
Once both barrels are full, incoming water still needs somewhere to go.
The final overflow should carry excess water to a suitable discharge location.
Do not simply let the last barrel spill next to a building foundation.
The Overflow Still Matters
Connecting two barrels doubles storage only until both barrels are full.
After that, additional roof runoff needs a controlled path out of the system.
The overflow should generally be able to handle water arriving faster than the barrels can store it.
It should also be positioned so that water does not:
- Pool around foundations
- Erode soil
- Flood walkways
- Flow toward basements or crawl spaces
- Undermine the barrel base
If your downspout receives large amounts of roof runoff, the overflow system can be just as important as the connection between the barrels.
Keep Mosquitoes and Debris Out
Connecting barrels creates additional openings that need to remain protected.
Roof runoff can carry leaves, grit, pollen, insects, bird droppings, and other contamination into storage.
Use appropriate inlet screening and keep lids and unused openings closed.
If the system includes a first-flush device, it diverts an initial portion of dirty roof runoff before later runoff enters storage. It can reduce some contamination entering the barrel, but it does not make the stored water safe to drink.
Inspect screens, gutters, and connecting lines regularly. A blocked balance line can make one barrel fill much faster than expected.
Watch for Sediment in Low Connections
One disadvantage of connecting barrels near their bottoms is that sediment naturally settles there.
Fine material entering from the roof can collect in the bottom of the first barrel and eventually enter the connecting line.
You can reduce problems by:
- Keeping gutters reasonably clean
- Using suitable inlet screening
- Keeping the connection slightly above the barrel floor
- Inspecting the connecting line during cleaning
- Removing accumulated sediment periodically
If flow between the barrels becomes noticeably slower, check for blockage before assuming the fittings or barrel heights are the problem.
What If One Barrel Is Higher Than the Other?
A small difference in base height usually does not prevent a bottom connection from working, but it changes how the system behaves.
The important measurement is the elevation of the water surfaces and outlets, not simply whether the barrels look level beside each other.
If one barrel is significantly higher, the lower barrel may reach its maximum level before the higher barrel is full.
For the simplest balanced system, place the barrels on the same stable, level platform or on separate bases that put them at similar elevations.
Never use an unstable stack of blocks just to correct the height.
Can You Connect Different-Size Rain Barrels?
Yes.
The barrels do not need to have the same capacity.
For example, you could connect a smaller barrel to a larger storage tank if their fittings and elevations allow water to move correctly.
With a bottom balance connection, the water surfaces can still settle at approximately the same height. The larger barrel simply stores more water at each level because it has more internal volume.
Pay attention to:
- Different barrel heights
- Different wall shapes
- Outlet elevations
- Fitting compatibility
- Maximum safe fill levels
- Overflow location
Two barrels with matching capacities are usually easier to arrange, but matching size is not required.
Can You Add a Third or Fourth Barrel?
Yes. The same idea can be extended to several barrels.
You can connect them in a row or use a manifold that feeds several tanks.
As the system grows, though, connection size and layout become more important.
A small hose that works well between two barrels may not transfer water quickly enough through a larger bank of barrels during heavy rain.
More barrels also mean:
- More fittings that could leak
- More stored weight
- More surfaces to clean
- More valves and connections to inspect
- A larger overflow requirement
For a large storage system, a purpose-built cistern may eventually become simpler than maintaining many small barrels.
Using Connected Barrels for Irrigation
Connected barrels work well for watering gardens, but joining the barrels does not create much additional pressure.
Gravity pressure comes mainly from the vertical distance between the water surface and the outlet.
This vertical difference is often called head height.
Adding another barrel increases stored volume. It does not significantly increase pressure if both barrels remain at the same height.
If you are feeding drip irrigation, sprinklers, or a long garden hose, check the pressure and flow rate the equipment requires.
Flow rate is the amount of water moving through the system over time, often measured in gallons per minute.
Some low-pressure irrigation equipment works well with elevated rain barrels. Other equipment requires more pressure and may need a properly selected pump.
Do Not Treat Connected Rain Barrels as Drinking-Water Treatment
Joining two barrels changes storage capacity, not water quality.
Roof runoff may contain microorganisms, animal waste, roofing debris, metals, chemicals, or other contaminants.
Water intended for drinking requires a suitable collection system, appropriate treatment stages, ongoing maintenance, and current laboratory testing. Local rules may also apply.
A screen, sediment filter, first-flush diverter, or single treatment device should not be treated as proof that roof-collected rainwater is potable.
Potable means suitable for drinking. Water used for irrigation or other uses where drinking-water quality is not required is generally considered non-potable.
Keep any rainwater plumbing separated from household drinking-water plumbing unless the system has been designed to meet applicable plumbing and public-health requirements.
Common Problems After Connecting Two Barrels
The Second Barrel Fills Very Slowly
Check the balance or transfer line for:
- Sediment
- Kinks
- Closed valves
- Undersized hose
- Blocked fittings
- Poor hose routing
A narrow line can also struggle to keep up with fast roof runoff even when nothing is blocked.
One Barrel Is Much Fuller Than the Other
For bottom-connected barrels, check whether the balance line is blocked or whether the barrels sit at very different elevations.
For top-connected barrels, different water levels are normal because the first barrel must reach the transfer opening before filling the second.
A Bulkhead Fitting Leaks
Drain the water below the fitting before working on it.
Check whether:
- The gasket is seated correctly
- The barrel wall is flat
- The hole is the correct size
- The fitting is damaged
- The connection was overtightened
- The attached pipe is pulling sideways on the fitting
Simply tightening harder can make some leaks worse.
The First Barrel Overflows Before the Second Is Full
The transfer line may be too small or restricted.
The problem can also occur when the inlet delivers water faster than the connecting line can move it.
The system's final overflow should still provide a safe path for excess water.
Plan for Cleaning and Cold Weather
Design the connection so you can eventually take it apart.
Barrels need periodic inspection and cleaning, especially around low outlets where sediment accumulates.
If your area experiences freezing temperatures, exposed barrels, valves, hoses, and fittings can be damaged when trapped water freezes and expands.
A freeze strategy depends on the barrel material, plumbing layout, climate, and how the system is used. In some climates, the safest seasonal approach is to drain and disconnect vulnerable components before sustained freezing weather.
Do not rely on a valve being closed as proof that a fitting or hose contains no trapped water.
Frequently Asked Questions
Should I connect rain barrels at the top or bottom?
Connect them near the bottom if you want the barrels to fill and drain together. Connect them near the top if you want the first barrel to fill before sending overflow into the next one.
Can I connect two rain barrels with a garden hose?
A garden hose can sometimes serve as a balance line if you have suitable fittings, but its small inside diameter may limit how quickly water moves between barrels. A larger hose or pipe may work better when the barrels receive high runoff flow.
Do connected rain barrels need to be the same height?
For a bottom-balanced system, keeping the barrels at similar elevations makes the system easier to use and allows their storage volumes to work together predictably. The barrels themselves do not have to be identical.
Can two rain barrels share one spigot?
Yes. If the barrels are connected near the bottom, water from the second barrel can move toward the first as water leaves the shared outlet. The connecting line must remain open and capable of supplying the required flow.
Does connecting two rain barrels increase water pressure?
It mainly increases storage capacity, not pressure. Gravity pressure depends largely on head height, which is the vertical distance between the water surface and the outlet.
Does the second barrel need an overflow?
The system needs a final overflow after the last barrel. In a two-barrel cascading setup, this normally means providing the second barrel with a controlled overflow once both barrels are full.
How far apart can connected rain barrels be?
There is no single correct distance. Short connections are generally simpler and have less flow resistance. Longer runs need careful attention to hose diameter, elevation, support, bends, and protection from damage.
Can connected rain barrels be used for drinking water?
Connecting barrels does not make roof runoff safe to drink. Drinking-water use requires suitable collection, treatment, maintenance, current laboratory testing, and compliance with applicable local requirements.
