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A rain barrel is usually plumbed with three main connections: an inlet for rainwater, an outlet near the bottom, and an overflow near the top. The outlet can feed a hose or garden line by gravity. The overflow should carry extra water away from the house when the barrel is full.
Good plumbing matters because a poorly placed fitting can leak, an undersized overflow can cause water to spill near the foundation, and a garden line may not work well if the barrel does not provide enough pressure.
The Basic Rain Barrel Plumbing Layout
A simple setup looks like this:
- Roof runoff enters through a downspout or rain barrel diverter.
- A screened opening keeps large debris and mosquitoes out.
- Water collects inside the barrel.
- A lower outlet supplies a hose or irrigation line.
- An upper overflow sends extra water to a safe drainage area.
Some systems also connect two or more barrels together.
Before drilling any holes, decide where each connection needs to go. Changing the plumbing later often means patching old holes.
Choose a Good Location First
Place the barrel on a firm, level base close to the downspout you plan to use.
A full barrel is very heavy. Water weighs about 8.3 pounds per US gallon. A 55-gallon barrel can therefore hold more than 450 pounds of water, not including the barrel itself.
Use a base that can safely support the filled barrel without settling or tipping.
You may want to raise the barrel slightly so a watering can fits under the outlet or so gravity can move water through a hose. Do not build a tall or unstable stand just to gain pressure. A large elevated tank needs a properly designed support structure.
Also leave enough space to reach the fittings for cleaning and repairs.
Plan the Inlet
There are two common ways to send downspout water into a barrel.
Open-Top Inlet
With this setup, the downspout ends above a screened opening in the barrel lid.
The screen catches leaves and helps keep insects out.
The opening should be large enough to accept the expected flow without causing water to back up around the downspout.
This design is simple, but the screen needs regular cleaning.
Downspout Diverter
A diverter is installed in the downspout and sends some rainwater through a hose into the barrel.
Many diverters are designed so excess water continues down the original downspout when the barrel fills.
Follow the diverter manufacturer's installation height and hose-size instructions. Different designs handle a full barrel in different ways.
Do not assume a diverter removes the need to think about overflow. Make sure you understand where water will go after the barrel is full.
Install the Lower Outlet
The lower outlet is where you connect a spigot, hose, or irrigation line.
Place it close to the bottom of the barrel, but not necessarily at the absolute lowest point.
Leaving a small space below the outlet lets heavy sediment settle where it is less likely to enter the hose.
Use a Watertight Tank Fitting
A bulkhead fitting is a fitting that passes through the wall of a tank and seals around the hole. It usually has a threaded body, gasket, and retaining nut.
Bulkhead fittings provide a better connection than simply pushing a tap through a drilled hole.
Another option is a fitting specifically designed for rain barrels or tanks that can be installed through the barrel wall.
Whatever fitting you use, make sure:
- It is intended for the barrel material.
- The hole matches the fitting size.
- The gasket sits flat.
- The barrel wall is smooth around the hole.
- The fitting is not overtightened.
Too much tightening can deform a plastic barrel or squeeze a gasket out of place.
Drill the Hole Carefully
Check the fitting manufacturer's required hole size before drilling. The nominal pipe size is often not the same as the hole diameter.
For example, a fitting sold for a certain pipe size may require a noticeably larger hole through the barrel.
Drill on a flat part of the barrel wall rather than across a molded ridge or seam.
Remove plastic shavings and rough edges before installing the fitting.
Attach the Spigot or Hose Connection
Once the tank fitting is installed, you can attach the outlet hardware.
A common arrangement is:
barrel → bulkhead fitting → valve or spigot → garden hose
If the threaded parts require thread seal tape or another sealant, use one that is suitable for the fitting material and follow the fitting instructions.
Do not try to fix a poorly fitted gasket by adding large amounts of sealant around the outside. The mechanical fitting should provide the main seal.
A shutoff valve is useful even if the final connection is a hose. It lets you stop the water while changing hoses or irrigation parts.
Understand Gravity Pressure
Most rain barrels do not produce the pressure you get from a household faucet.
Water pressure depends largely on the vertical distance between the water surface and the point where the water is being used. This vertical distance is sometimes called head height.
One foot of water height provides only about 0.43 psi of pressure.
That means a small barrel sitting close to ground level may provide only a few pounds per square inch, and the pressure falls as the barrel empties.
This is usually enough for:
- Filling a watering can
- Slow hose watering
- Some gravity-fed drip systems
It may not be enough for:
- Standard lawn sprinklers
- Long narrow hoses
- Pressure-compensating irrigation equipment with higher minimum pressure needs
- Irrigation systems designed for household water pressure
Check the pressure and flow needs of any irrigation equipment before connecting it.
Keep the Outlet Line Simple
Gravity systems work best when water has an easy path to follow.
Long hoses, small tubing, filters, valves, elbows, and elevation changes all reduce flow.
Flow rate means the amount of water moving through the system over a certain time, such as gallons per minute.
If your barrel drains very slowly, the problem may not be the barrel. A narrow fitting, clogged screen, restrictive filter, or long hose can limit the flow.
Use pipe and hose sizes that make sense for the amount of water you need to move.
Install an Overflow Connection
Overflow plumbing is one of the most important parts of a rain barrel.
Once the barrel is full, every additional gallon entering the barrel must have somewhere to go.
Place the overflow fitting near the top of the barrel while leaving enough plastic around the opening for the fitting and gasket to seal properly.
Connect the overflow to a hose or pipe that carries water to an appropriate drainage location.
The overflow should normally discharge away from:
- The house foundation
- Basement walls
- Crawl spaces
- Septic system components
- Areas where erosion could occur
- Places where standing water creates a problem
Do not reduce a large incoming flow to a tiny overflow hose without considering how quickly water may arrive during heavy rain.
If water enters faster than the overflow can carry it away, the barrel can spill over.
Keep Mosquitoes Out of the Plumbing
Any opening that reaches the stored water can become an insect entry point.
Screen exposed openings with a fine, durable insect screen where practical. Pay attention to:
- The inlet
- Overflow outlet
- Vents
- Open pipe connections
Make sure screens do not become so clogged with leaves and dirt that they block water flow.
Understanding DIY rain barrel designs helps assess tank material choices for the intended end use.
A closed diverter system may reduce open access, but connections still need regular inspection.
Connecting Two Rain Barrels
You can increase storage by plumbing two barrels together.
There are two common arrangements.
Connecting Near the Bottom
A pipe or hose connects the barrels at a low point.
As water enters one barrel, the water levels in the connected barrels tend to equalize.
This arrangement can allow one outlet to draw from both barrels.
Both connection points should be at about the same height, and the line between them should not be unnecessarily restrictive.
A valve on each barrel can make maintenance easier.
Connecting Near the Top
You can also let the first barrel overflow into the second.
This is easier in some installations, but the barrels fill in sequence rather than acting as one large equalized tank.
The final barrel still needs an overflow route.
Add a Drain If It Helps With Cleaning
A normal spigot placed slightly above the bottom may leave sediment and water behind.
If you want easier cleaning, you can install a separate low drain at a location where it can be safely reached.
The drain should have a secure cap or valve.
Do not place a fitting so low that there is not enough flat barrel wall around it to seal reliably.
Periodic draining and cleaning can remove sediment that collects below the normal outlet.
Consider a First-Flush System
Roof runoff can carry dust, pollen, leaves, bird droppings, and other debris.
A first-flush diverter is a device intended to divert some of the initial roof runoff before the cleaner portion of the rainfall enters storage.
It can reduce the amount of debris entering a barrel, but it does not make stored rainwater safe to drink.
A first-flush device also needs cleaning and draining according to its design.
For basic garden watering, some systems use simpler roof and gutter screening instead. The right approach depends on the roof, intended use, and maintenance you are willing to do.
Test the Plumbing Before the Next Storm
You do not need to wait for heavy rain to find a leak.
Partly fill the barrel with water and inspect every connection.
Look around:
- The lower bulkhead fitting
- The spigot
- Connection hoses
- Barrel-to-barrel fittings
- The overflow fitting
Open the outlet and make sure water flows correctly.
You can also carefully add water near the top to confirm that the overflow carries water where you intended.
If a bulkhead leaks, drain the water below the fitting before adjusting it. Do not keep tightening a plastic fitting in an attempt to stop every leak. Check the gasket position, hole condition, and fitting compatibility first.
Plumbing a Rain Barrel to Drip Irrigation
A rain barrel can feed some drip irrigation systems, but equipment compatibility matters.
Many irrigation parts are designed for much higher pressure than a barrel can provide.
A basic gravity system usually works best with:
- Short runs
- Relatively large supply tubing
- Low-pressure emitters or outlets
- Few restrictive fittings
- Limited elevation gain
Filters may be useful because small irrigation openings can clog with sediment. However, a filter also creates resistance and must be cleaned.
If you need reliable pressure over a large irrigation area, a pump may be more practical than trying to solve the problem by placing the barrel on a very tall stand.
When a Pump Is Needed
A pump may be useful when you need to move water uphill, through long pipes, or through equipment that requires more pressure.
Choosing a pump involves more than matching the hose size.
You need to consider:
- Required flow
- Required pressure
- Vertical lift
- Pipe losses
- Pump inlet conditions
- Available electrical power
- Dry-run protection
- Weather exposure
- Freeze conditions
Electrical equipment around water needs suitable protection and installation. Have a qualified professional handle electrical work when required.
Do Not Connect a Rain Barrel Directly to Drinking-Water Plumbing
A basic rain barrel should be treated as a non-potable water source.
Non-potable means the water is not intended for drinking.
Do not make a direct connection between a rain barrel system and household drinking-water plumbing unless the system has been professionally designed with the required treatment, backflow protection, and plumbing safeguards.
A simple screen, sediment filter, carbon filter, or UV unit by itself does not establish that roof-collected rainwater is safe to drink.
Using harvested rainwater for drinking requires a whole-system approach that considers the collection surface, contaminants, storage conditions, treatment stages, current laboratory testing, maintenance, and applicable local requirements.
Protect the Plumbing in Freezing Weather
Water trapped inside fittings, hoses, valves, and barrels can freeze and expand.
In freezing climates, prepare the system before sustained freezing weather.
Depending on the setup, this may mean draining:
- The barrel
- Exposed hoses
- Filters
- Pumps
- Valves
- Connecting pipes
Disconnect or bypass downspout plumbing if necessary so winter runoff still has a safe drainage path.
Do not assume a flexible hose or plastic barrel cannot be damaged by freezing water.
A Simple Plumbing Checklist
Before putting your rain barrel into regular use, check that:
- The barrel sits on a stable, level base.
- Roof water can enter without backing up.
- The inlet is protected from large debris and insects.
- The lower outlet fitting does not leak.
- The shutoff valve is easy to reach.
- The hose or irrigation system works with the available gravity pressure.
- The overflow can handle incoming water.
- Overflow water drains safely away from the building.
- Every barrel in a multi-barrel system has a safe overflow path.
- Plumbing can be drained or protected when freezing weather arrives.
A simple rain barrel does not need complicated plumbing. A secure inlet, a well-sealed lower outlet, and a properly routed overflow are the main parts to get right.
Frequently Asked Questions
Where should the spigot go on a rain barrel?
Place the spigot near the bottom so you can use most of the stored water. Leaving a little space below the outlet gives sediment somewhere to settle and provides enough flat barrel wall for a secure fitting.
What fitting should I use through a rain barrel wall?
A bulkhead fitting or another fitting specifically made for tanks and rain barrels is usually a good choice. It passes through the barrel wall and seals with a gasket. Match the fitting to the barrel material and drill the hole to the size specified by the fitting manufacturer.
Can I connect a garden hose directly to a rain barrel?
Yes, if the outlet has compatible garden-hose threads or an adapter. Keep in mind that the hose will receive much less pressure than it normally gets from a household faucet.
Why does water come out of my rain barrel so slowly?
Low water height, a small outlet, a long hose, clogged screens, filters, narrow tubing, or an uphill run can all reduce flow. Rain barrels rely mainly on gravity unless a pump is added.
How large should the rain barrel overflow be?
The overflow should be able to carry incoming water away fast enough when the barrel is full. The required capacity depends on the roof area, rainfall intensity, inlet arrangement, and plumbing layout. Avoid routing a large downspout flow through a very small hose without checking whether it can keep up.
Can I connect several rain barrels to one downspout?
Yes. Barrels can be connected near the bottom so their water levels equalize, or the overflow from one barrel can feed the next. The final system still needs a safe overflow route.
Can rain barrel water be connected to my home's plumbing?
A basic rain barrel should not be directly connected to household drinking-water plumbing. Cross-connections can create contamination risks. More complex household rainwater systems need suitable separation, backflow protection, treatment, and compliance with local plumbing requirements.
Do I need a pump for a rain barrel?
Not for basic watering if gravity provides enough flow. A pump becomes useful when you need higher pressure, longer pipe runs, uphill delivery, or irrigation equipment that cannot operate at rain-barrel pressure.
