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Saving rainwater can be as simple as placing a covered barrel under a downspout or as involved as installing a large underground cistern. The best method depends on how much water you want to collect, how you plan to use it, and how much space you have.
For most homes, the easiest place to start is the roof. Gutters already collect rain from a large surface and can direct it into storage for gardens, landscaping, cleaning, and other suitable non-potable uses.
1. Collect Rainwater in a Rain Barrel
A rain barrel is one of the simplest ways to save roof runoff.
The barrel connects to a downspout and stores water that would otherwise flow onto the ground or into a storm drain. Common uses include:
- Watering flowers and shrubs
- Filling watering cans
- Supplying a low-pressure drip or soaker line
- Outdoor cleaning where untreated rainwater is appropriate
Keep the barrel covered and screened so leaves, animals, and mosquitoes cannot easily enter.
A full barrel is very heavy, so place it on a firm, level base. If you raise it for better gravity flow, use a stand designed to support the full weight safely.
2. Connect Several Rain Barrels Together
One barrel may fill quickly during a good storm. Connecting several barrels can increase storage without installing one very large tank.
Barrels can be connected near the top so excess water flows from one barrel to the next. They can also be connected lower down so the water levels tend to equalize.
Lower connections can make the barrels behave more like one storage system, but every connection becomes another potential leak point.
Whichever setup you use, make sure:
- The fittings are compatible with the barrel walls.
- Connecting hoses are large enough for the expected flow.
- All containers sit on stable bases.
- The system has a safe overflow route.
3. Install a Larger Above-Ground Water Tank
If rain barrels do not provide enough capacity, an above-ground tank can store much more roof runoff.
These tanks may be used beside a house, barn, shed, greenhouse, or other suitable collection building.
Before choosing one, check more than capacity. You also need to consider:
- Tank dimensions
- Available installation space
- Inlet and outlet locations
- Overflow size
- Access for cleaning
- Foundation requirements
- Pump or gravity-feed connections
- Freezing conditions
Water weighs about 8.3 pounds per U.S. gallon, so even a moderately sized tank creates a major load. The base must be able to support the tank when it is completely full.
4. Reuse an IBC Tote for Rainwater Storage
An IBC tote can provide more storage than a typical rain barrel and is often used for garden irrigation or other non-potable applications.
Only use a tote when you know its previous contents. A container that once held an unknown or hazardous substance may not be suitable for water storage.
You should also protect the water from light where practical. Sunlight can encourage algae growth inside translucent containers.
Check the tote's:
- Valve type
- Thread or adapter size
- Lid condition
- Cage and pallet condition
- Previous use
- Structural condition
Do not assume every hose fitting or pump fitting will connect directly to an IBC outlet. Adapters are often needed.
5. Install a Cistern
A cistern is a larger storage tank designed to hold collected water. It may be installed above ground or underground.
Cisterns make sense when you want to capture more of the water available from a larger roof or when you expect longer periods between rainfall.
A complete cistern system may include:
- Gutters and downspouts
- Leaf screens
- A first-flush device
- A tank inlet
- Storage
- An overflow
- A pump
- Filtration or treatment appropriate for the intended use
A first-flush device diverts some of the first runoff from the roof. This can reduce the amount of dust, droppings, pollen, and other debris entering storage.
Underground cisterns require careful planning. Excavation, groundwater pressure, tank specifications, access, drainage, and structural loading can make installation more than a simple DIY project.
6. Save Rainwater in a Garden Pond
A properly designed garden pond can hold some rainfall and runoff while also serving as a landscape feature.
This is different from storing clean roof runoff in a closed tank. Pond water is exposed to:
- Soil
- Wildlife
- Insects
- Plants
- Algae
- Windblown debris
That makes it more suitable for landscape purposes than uses requiring cleaner stored water.
Make sure overflow from the pond has somewhere safe to go during heavy rain. Do not direct excess water toward foundations, neighboring property, septic systems, or areas that are easily eroded.
7. Build Swales to Hold Rainwater in the Landscape
You do not have to put rainwater in a container to save it.
A swale is a shallow landscape feature that slows runoff and gives water more time to soak into the soil. It can be useful around gardens, trees, and larger planting areas.
Swales work best when they follow the shape and slope of the land rather than simply acting as drainage trenches.
Their goal is usually to slow, spread, and soak water rather than move it away as quickly as possible.
Be cautious on steep slopes or near buildings. Poorly placed earthworks can send water where you do not want it.
8. Create a Rain Garden
A rain garden is a planted area designed to temporarily receive runoff and allow much of it to soak into the ground.
It can collect water from:
- Downspouts
- Driveway edges
- Patio runoff
- Other suitable drainage areas
A rain garden normally does not hold standing water permanently. Instead, it receives water after rain and gradually drains.
Plant and soil choices depend on local conditions, including how quickly the soil drains.
Keep rain gardens far enough from foundations and other sensitive areas. Local drainage and stormwater rules may also affect where they can be built.
9. Use Mulch to Keep Rainwater in the Soil
Saving rainwater also means preventing it from evaporating too quickly after it reaches your garden.
Mulch helps by covering the soil surface. It can reduce evaporation and help keep soil moisture more stable between rainstorms.
Common garden mulches include:
- Wood chips
- Shredded bark
- Leaves
- Straw suitable for garden use
- Other locally appropriate organic materials
Mulch does not increase the amount of rain that falls, but it can help you make better use of the water already in the soil.
It can be especially useful when combined with stored rainwater and drip irrigation.
10. Direct Roof Runoff Into the Soil
Not every downspout needs to feed a tank.
Evaluate simple garden rainwater collection methods to evaluate emitter flow under available pressure and pump capacity.
Where site conditions allow, you may be able to direct roof runoff toward planted areas, trees, swales, or rain gardens instead of sending it immediately to a storm drain.
The important part is controlling where the water goes.
Do not simply disconnect a downspout if the runoff could collect beside the foundation or cause erosion.
A good drainage route should handle overflow during heavy rain, not just small showers.
How Much Rainwater Can a Roof Collect?
Your roof size and rainfall determine how much water is potentially available.
For U.S. measurements, a useful estimate is:
Gallons collected = roof area in square feet × rainfall in inches × 0.623
For example, 500 square feet of roof receiving 1 inch of rain has a theoretical yield of:
500 × 1 × 0.623 = about 312 gallons
You will usually collect less than the theoretical amount.
Water can be lost through:
- Initial roof wetting
- First-flush diversion
- Gutter overflow
- Splashing
- Leaks
- Filters and screens
- Tank overflow
This calculation can help you see why a small rain barrel may fill very quickly during a storm.
Choose Storage Based on How You Will Use the Water
Before building a collection system, decide what the water is for.
For garden watering, a simple screened barrel may be enough.
For a larger irrigation system, you may need a bigger tank, pump, filter, and properly sized plumbing.
Indoor uses require much more planning because untreated roof runoff can contain microorganisms, animal waste, chemicals, metals, and other contaminants.
Rainwater intended for drinking should not be treated as safe simply because it looks clear. Potable use requires a suitable collection system, appropriate treatment stages, maintenance, current water testing, and compliance with applicable local requirements.
Potable means suitable for drinking. Non-potable means water that is not considered drinking water.
Do Not Forget the Overflow
Every rainwater storage system eventually fills.
Once that happens, incoming water needs a controlled path away from the tank.
A good overflow should:
- Handle incoming stormwater without easily backing up.
- Discharge where water can drain safely.
- Avoid foundations and structures.
- Avoid causing erosion.
- Be screened where insects or animals could enter the tank through it.
Overflow planning is just as important as storage capacity.
A 50-gallon barrel connected to a large roof can fill long before the storm ends.
Keep Collected Rainwater Cleaner
Storage works better when you keep debris out from the start.
Depending on your system, useful measures can include:
- Keeping gutters clean
- Using leaf screens
- Screening tank openings
- Using a first-flush device where appropriate
- Keeping storage covered
- Preventing animals from entering
- Keeping sunlight out of the tank where practical
- Cleaning accumulated sediment when needed
Filters and screens need regular inspection. A clogged screen can cause water to bypass the collection system or overflow from the gutter.
Protect the System in Freezing Weather
Water expands when it freezes. That can damage barrels, filters, valves, hoses, pumps, and exposed pipes.
In climates with hard freezes, seasonal systems may need to be drained and disconnected before winter.
Larger year-round systems may require more involved freeze protection based on the tank, plumbing, pump location, and local climate.
Do not assume that wrapping an exposed pipe or barrel will guarantee protection during prolonged freezing weather.
Start With the Simplest Method That Meets Your Needs
You do not need a large cistern to begin saving rainwater.
For many homeowners, a practical starting system is simply:
Roof → gutter → screened downspout connection → covered rain barrel → controlled overflow
If you regularly run out of stored water, you can add capacity later.
The best rainwater system is not necessarily the one that stores the most water. It is the one that provides enough usable water for your intended purpose without creating difficult maintenance, drainage, structural, or water-quality problems.
Frequently Asked Questions
What is the easiest way to save rainwater?
A covered rain barrel connected to a roof downspout is usually one of the easiest options. Make sure it has a screened inlet, a stable base, and a controlled overflow.
Can I collect rainwater without a tank?
Yes. Swales, rain gardens, mulch, and carefully directed downspouts can help keep rainfall in the landscape instead of storing it in a container.
How many gallons can I collect from 1 inch of rain?
About 0.623 gallon of water falls on each square foot of horizontal collection area during 1 inch of rain. Multiply your roof collection area in square feet by 0.623 to estimate theoretical yield. Actual collection will be lower because of system losses.
Can I connect two rain barrels together?
Yes. Rain barrels can be connected with suitable fittings and hoses. You still need enough overflow capacity because both barrels can eventually become full.
Can saved rainwater be used for drinking?
Do not assume untreated roof runoff is safe to drink. Drinking-water systems require suitable collection, treatment, maintenance, current water testing, and compliance with applicable local requirements.
Should a rainwater tank be covered?
Yes. A closed or properly covered tank helps keep out debris, animals, insects, and sunlight. Openings and vents may still be needed, but they should be designed so unwanted material cannot easily enter.
What should I do when my rain barrel is full?
Excess water should leave through a properly sized overflow and discharge somewhere that can handle it safely. Keep overflow away from foundations and areas where it could cause erosion or flooding.
