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A rain barrel is a simple way to collect roof runoff and use it for garden watering. The basic setup is a covered barrel connected to a downspout, with a screened inlet, an overflow outlet, and a spigot near the bottom.
The most important parts are not complicated. Keep debris and mosquitoes out. Give excess water a safe place to go. Make sure the barrel sits on a strong, level base. And remember that collected rainwater is non-potable, which means it should not be treated as drinking water.
What You Need to Make a Rain Barrel
For a basic garden rain barrel, you will need:
- A clean, sturdy barrel with a lid
- A downspout that drains part of your roof
- A screened inlet or downspout diverter
- A spigot or hose connection
- An overflow fitting and hose
- Washers or seals made for the fittings you use
- A solid, level base
- Basic hand tools for drilling and tightening fittings
A commonly used barrel holds around 50 to 60 gallons, but you can use another size if it fits your space.
Do not reuse a container that previously held fuel, pesticides, solvents, or other hazardous chemicals. A used food-grade container may be suitable if you know what it held and can clean it properly.
Choose the Right Location
Place the barrel near a downspout that receives useful roof runoff.
Before installing anything, look at the area during or after a heavy rain. Check where water normally goes. Your barrel's overflow will eventually need to drain somewhere safe.
The site should be:
- Firm and level
- Easy to reach with a watering can or garden hose
- Close enough to the downspout for a simple connection
- Away from places where overflow could enter a basement or damage a foundation
A full barrel is very heavy. Water weighs about 8.3 pounds per U.S. gallon. That means 55 gallons of water alone weighs about 457 pounds, before adding the barrel and hardware.
Do not place a filled barrel on an unstable stack of loose blocks or another base that could shift.
Prepare a Strong Base
Raising the barrel can make the spigot easier to use and can provide a little more water pressure.
Gravity pressure depends mainly on head height. Head height is the vertical distance between the water level in the barrel and the point where the water comes out.
A barrel sitting only a little above the garden will produce low pressure. That is usually fine for filling watering cans or feeding a short, simple hose. It may not be enough for equipment that needs steady pressure.
Build or use a base that can safely support the barrel when it is completely full. Keep the top level so the barrel does not lean.
Install the Spigot
Put the spigot near the bottom of the barrel, but not at the absolute lowest point.
Leaving a small space below the outlet allows some sediment to settle without immediately entering your hose.
The exact hole size depends on the fitting you use. Follow the fitting manufacturer's required hole size rather than guessing.
Some rain barrels use a bulkhead fitting. A bulkhead fitting passes through the barrel wall and uses seals to make a watertight connection.
Install the fitting according to its instructions. Avoid overtightening plastic parts because that can deform seals or crack the barrel.
After installation, add a small amount of water and check the fitting for leaks before filling the barrel completely.
Create a Screened Inlet
Roof runoff can carry leaves, twigs, insects, grit, pollen, bird droppings, and other material.
Your inlet should have a screen that blocks larger debris and prevents mosquitoes from entering the barrel.
The screen should be:
- Securely attached
- Fine enough to block mosquitoes
- Easy to remove or reach for cleaning
- Large enough that normal flow does not immediately overwhelm it
Clean the screen whenever debris begins to collect.
A clogged inlet can cause water to back up or spill where you do not want it.
Connect the Downspout
There are two common ways to direct water into a barrel.
Direct Downspout Connection
You can shorten or redirect the downspout so water enters through the screened top of the barrel.
This method is simple, but you must provide a dependable overflow route. Once the barrel is full, every additional gallon needs somewhere else to go.
Downspout Diverter
A diverter is installed in the downspout and sends some roof runoff into the barrel.
Many diverter systems are designed so excess water continues down the original downspout after the barrel fills. Installation varies by design, so follow the diverter instructions carefully.
Do not assume every diverter works the same way.
Add an Overflow Outlet
An overflow is one of the most important parts of a rain barrel.
A barrel can fill quickly during a strong storm. Without a large enough overflow path, water may spill over the top or back up around the downspout.
Install the overflow near the top of the barrel.
Attach a hose or pipe that carries excess water to a safe drainage area. Keep the discharge away from foundations and other places where concentrated runoff could cause problems.
The overflow should be able to handle substantial flow. A tiny hose may not keep up with water arriving from a large roof section during heavy rain.
How Quickly Will a Rain Barrel Fill?
It often takes less rain than people expect.
A rough rainwater yield formula is:
Gallons collected = roof area in square feet × rainfall in inches × 0.623
For example, 200 square feet of roof receiving 1 inch of rain has a theoretical yield of:
200 × 1 × 0.623 = about 125 gallons
You will usually collect less than the theoretical amount. Some water is lost to wetting the roof, splashing, leaks, debris removal, and other parts of the system.
Even with those losses, a 50- or 60-gallon barrel connected to a useful roof area can fill during one storm.
That is why overflow planning matters.
Consider a First-Flush System
A first flush device diverts the first portion of runoff away from storage.
The beginning of a storm can wash more dust, droppings, pollen, and loose debris from the roof. Diverting some of this first runoff can reduce the amount entering your barrel.
A first-flush device is not a complete water treatment system. It also does not make roof runoff potable.
For a simple ornamental garden barrel, many homeowners use basic debris screening instead. Whether a first-flush device is useful depends on the roof, surrounding trees, intended use, and the amount of maintenance you are willing to do.
Test the Barrel Before Using It
Evaluate rain barrel collection mechanics to understand storage capacity against realistic use and replenishment.
Do not wait for a major storm to discover a bad connection.
Add water slowly and check:
- The spigot for leaks.
- The inlet connection.
- The overflow fitting.
- The barrel base for movement or leaning.
- The overflow route.
Then open the spigot and make sure water flows where expected.
Some seepage problems can be fixed by adjusting or reseating a fitting. If the barrel itself is cracked, replace or properly repair it rather than relying on a temporary patch that may fail when the barrel is full.
How to Use Rain Barrel Water in the Garden
The simplest method is to fill a watering can from the spigot.
You can also connect a garden hose, but flow will usually be much weaker than water from a household faucet.
Keep hose runs short where possible. Long hoses, narrow tubing, filters, valves, and elevation changes can reduce flow even more.
For gravity-fed drip irrigation, check the irrigation equipment carefully. Some drip systems need more pressure than a low rain barrel can provide.
Using Rainwater Around Edible Plants
Roof runoff is not automatically clean just because it came from rain.
Water may pick up contaminants from the roof, gutters, animal droppings, airborne debris, roofing materials, or dirty storage equipment.
For edible gardens, a cautious approach is to apply untreated collected rainwater to the soil rather than directly onto the parts of fruits, vegetables, or herbs that you plan to eat.
Do not use rain-barrel water as drinking water or for food preparation unless the entire collection and treatment system has been designed for potable use and the water has been appropriately tested.
Keep Mosquitoes Out
Standing water can become a mosquito breeding area if insects can reach it.
Keep the barrel closed and screen every opening that could allow mosquitoes inside. This includes the main inlet and, where needed, the overflow.
Check screens regularly for:
- Holes
- Gaps
- Loose edges
- Clogged debris
A good rain barrel should not depend on frequent chemical treatment to control mosquitoes. Physical exclusion is the better starting point.
Clean the Barrel and Gutters
A rain barrel needs regular maintenance.
Check the system after storms and during the watering season.
Clean:
- Gutters as needed
- Inlet screens
- Downspout strainers
- First-flush devices, if installed
- Overflow screens
- Sediment from the barrel when it builds up
Also look for algae growth, unusual odors, damaged fittings, leaks, insect access, or a leaning base.
Keeping the barrel shaded can reduce sunlight reaching the stored water and may help limit algae growth.
Prepare for Freezing Weather
Water expands when it freezes. A barrel or fitting full of frozen water can crack.
In climates with freezing winters, follow the barrel manufacturer's winter storage guidance. A common approach is to drain the barrel and disconnect or bypass it before sustained freezing weather arrives.
Also drain hoses, valves, and other parts that can trap water.
Do not assume that leaving the spigot open will protect every fitting from freeze damage.
Common Rain Barrel Mistakes to Avoid
A few setup problems cause many rain barrel headaches.
No Proper Overflow
A barrel without a safe overflow can send water toward the house when it fills.
Weak or Uneven Base
A full rain barrel can weigh several hundred pounds. A weak base can settle, tip, or collapse.
Open Inlets
Unscreened openings allow mosquitoes and larger debris into the water.
Expecting Household Water Pressure
A basic elevated rain barrel provides low gravity pressure. It will not normally behave like a pressurized outdoor faucet.
Using an Unknown Container
Do not store irrigation water in a used barrel if you do not know what was previously inside it.
Forgetting Maintenance
Screens, gutters, fittings, and sediment all need occasional attention. A rain barrel is simple, but it is not maintenance-free.
Frequently Asked Questions
How big should a rain barrel be for a garden?
There is no single best size. Consider your available space, roof area, rainfall, garden water use, and how often you can empty the barrel. A small barrel may fill quickly if it is connected to a large roof area.
Can I attach a garden hose to a rain barrel?
Yes, if the spigot has a compatible hose connection. However, gravity-fed water usually has much less pressure than a household outdoor faucet.
How high should I raise a rain barrel?
Raise it only as high as you can support safely on a strong, stable base. More height can improve gravity flow, but stability is more important than gaining a little extra pressure.
Does a rain barrel need an overflow hose?
Yes. Once the barrel is full, incoming roof runoff needs a safe route away from the barrel and your home's foundation.
Do I need a pump for garden watering?
Not always. Watering cans and some simple hose or low-pressure irrigation setups can work with gravity. A pump may be needed when the garden is uphill, farther away, or requires more pressure and flow.
Can mosquitoes breed in a covered rain barrel?
They can if mosquitoes find an opening. Keep the barrel closed and use well-fitted screens on openings that could allow insects inside.
Can I drink water collected in a garden rain barrel?
A basic garden rain barrel should be treated as a non-potable water system. Making roof runoff suitable for drinking requires appropriate collection materials, treatment, testing, maintenance, and compliance with applicable local requirements.
