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Rainwater can be collected from an asphalt shingle roof, but the safest use is generally non-potable use, such as watering ornamental plants or other jobs where people are unlikely to swallow the water.
Asphalt shingles should not be treated as a clean drinking-water catchment surface by default. Rain can pick up material from the roof itself along with dust, bird droppings, pollen, smoke particles, metals, and other contaminants. The CDC advises that collected rainwater can contain both germs and chemicals even when it looks clear.
If you want to use roof-collected water for drinking, cooking, bathing, or another use with more human contact, the roof is only one part of the decision. The whole collection, storage, treatment, testing, and plumbing system has to be suitable for that use.
What Happens When Rain Runs Over Asphalt Shingles?
Modern asphalt shingles are generally made with an asphalt-coated base, often fiberglass, and a surface layer of mineral granules.
That surface is designed to protect a house from weather. It was not necessarily designed or tested as a drinking-water collection surface.
As rain moves across the roof, it can collect material from several places:
- The shingle surface
- Roof dust and dirt
- Loose mineral granules
- Bird and animal droppings
- Leaves and pollen
- Air pollution that has settled on the roof
- Flashing around chimneys, valleys, and vents
- Gutters and downspouts
- Sealants, coatings, and repair materials
The CDC specifically notes that chemicals such as lead and copper can enter collected rainwater from roofing, gutters, pipes, storage materials, and other parts of the system.
An EPA rainwater-harvesting literature review also identified lead and mercury as contaminants of concern associated with asphalt-shingle runoff and noted that contamination can vary by roofing product. It recommended sampling water quality before choosing an end use.
This does not mean every asphalt roof produces dangerous concentrations of these contaminants. It means you cannot determine water quality simply by looking at the shingles.
Is Rainwater From Asphalt Shingles Safe for Garden Watering?
For ornamental plants, trees, lawns, and similar non-food landscaping, asphalt-shingle runoff is a much more practical use than drinking water.
A basic collection system should still keep debris and animals out of the stored water. At minimum, that usually means:
- Clean gutters
- A leaf or debris screen
- A covered barrel or tank
- Screened tank openings
- An overflow that drains safely
- Periodic tank and gutter cleaning
A first-flush diverter can also improve incoming water quality.
A first flush is the first portion of runoff during a rain event. It tends to wash accumulated dust, droppings, pollen, and other material from the roof. A first-flush diverter sends some of this initial runoff away from the storage tank.
The CDC recommends considering first-flush diversion because the first runoff can contain more dirt, germs, and chemicals.
A diverter improves the system, but it does not turn asphalt-roof runoff into drinking water. It also cannot reliably remove substances that continue entering the water as rain moves across roofing or other system components.
What about vegetable gardens?
Use more caution with crops that will be eaten, particularly vegetables and fruit eaten raw.
The CDC recommends using treated public water or bottled water when possible for plants intended for eating.
The concern is not limited to asphalt. Roof-collected water can pick up animal waste and other contamination regardless of the roof material.
If you plan to irrigate food crops with collected roof water, check guidance from your local health department or agricultural extension service. The appropriate use can depend on your roof, surrounding environment, irrigation method, crops, and local rules.
Can You Drink Rainwater From an Asphalt Shingle Roof?
Do not assume untreated rainwater from an asphalt-shingle roof is safe to drink.
Rainwater can contain microorganisms as well as chemicals. CDC guidance recommends regularly testing rainwater for both germs and chemicals when it is used for drinking, cooking, or bathing.
The roofing material adds another issue. A roof that performs well as a roof has not automatically been evaluated for collecting potable water.
For a drinking-water system, you need to consider the complete path:
roof → gutters → prefiltration → storage → treatment → plumbing → faucet
Every stage can affect water quality.
A filter alone is not enough
A sediment filter can remove particles. It does not necessarily remove dissolved chemicals or microorganisms.
An activated-carbon filter can address certain contaminants, tastes, or odors when it is designed for those contaminants. It does not automatically make microbiologically contaminated rainwater safe.
UV treatment can inactivate certain microorganisms when the system is correctly sized and the incoming water meets its operating requirements. UV does not remove dissolved chemicals.
For this reason, potable rainwater normally requires multiple treatment stages chosen for the actual contaminants and water conditions.
Regular laboratory testing is still needed. A simple home test strip or total dissolved solids meter cannot establish that roof-collected rainwater is safe to drink.
Does NSF Certification Matter?
It can matter when drinking-water collection is the goal.
NSF has a rainwater catchment testing program under NSF Protocol P151. The program evaluates rainwater catchment components, including roofing materials and coatings, for whether they introduce contaminants at levels exceeding applicable health guidelines under the test conditions.
If you are planning a potable rainwater system, do not assume that a roof is acceptable merely because the material is commonly used.
Check the exact roofing product and other water-contact components. Certification or testing applies to specific listed products and configurations, not automatically to every product made from the same general material.
Storage tanks and plumbing components intended for drinking-water contact may also have separate drinking-water certifications.
Does Roof Age Make a Difference?
Roof condition matters, but age by itself does not tell you whether the runoff is suitable for a particular use.
An older asphalt roof may have:
- Loose granules
- Moss or biological growth
- Accumulated debris
- Damaged shingles
- Old flashing
- Previous roof repairs
- Sealants or coatings of unknown composition
A newer roof may have different materials, treatments, flashing, and manufacturing formulations.
Because asphalt shingles vary by manufacturer and product, there is no simple age at which rainwater suddenly becomes safe or unsafe.
Inspect the complete roof rather than judging it only by age.
If you do not know what materials or coatings have been applied to the roof, avoid assuming that the runoff is suitable for higher-contact uses.
Watch the Other Parts of the Roof
The shingles are not the only surface touching your rainwater.
Account for contamination risks in fresh rainwater to compare component compatibility before materials are finalized.
Pay particular attention to:
Flashing
Roof flashing may be made from aluminum, galvanized steel, copper, lead, or other materials depending on the roof and its age.
Water may cross flashing around:
- Chimneys
- Roof valleys
- Vent pipes
- Skylights
- Wall intersections
This matters because metals can enter roof runoff.
Gutters and downspouts
Dirty gutters can hold leaves, insects, animal waste, roofing granules, and standing water.
Clean them regularly enough to keep material from washing into the tank.
Roof treatments
Be cautious if the roof has been treated with:
- Moss or algae chemicals
- Pesticides
- Roof cleaners
- Paint
- Sealants
- Field-applied coatings
Do not route runoff back into the tank until you know the product's instructions and suitability for your intended rainwater use.
Applying a coating to asphalt shingles simply to improve rainwater quality is not a good general solution. The Asphalt Roofing Manufacturers Association advises checking with the shingle manufacturer before applying field-applied coatings because coatings can affect the roofing system itself.
A Practical Setup for Non-Potable Collection
For garden or similar outdoor use, keep the system simple but controlled.
A typical flow might be:
asphalt roof → clean gutter → leaf screen → first-flush diverter → covered tank → irrigation outlet
The leaf screen keeps larger material out.
The first-flush diverter reduces some of the contamination washed from the roof at the start of a storm.
The covered tank limits entry by debris, animals, and insects. Blocking sunlight also helps reduce algae growth.
Screen all openings where mosquitoes could enter. The CDC recommends screening rainwater systems or regularly emptying small rain barrels to prevent mosquito breeding.
If you connect a pump or irrigation system, add filtration appropriate to the equipment. Small drip emitters, for example, can clog much more easily than an open-ended garden hose.
When You Should Avoid Collecting Roof Runoff
Temporarily disconnect or divert collection when the roof has recently been exposed to something you do not want in the tank.
Examples include:
- Roof-cleaning chemicals
- Moss or algae treatments
- Pesticide application
- Painting or coating work
- Roof repairs involving unknown sealants
- Heavy contamination from nearby construction
- Large amounts of animal waste
- Fire or heavy smoke deposition
Also inspect the roof after major storms or roofing work before reconnecting the tank.
Do not climb onto a roof merely to prepare it for rainwater collection unless you have the equipment and training to work safely at height. Many maintenance jobs can be handled from the ground or by a qualified roofing contractor.
If You Are Planning a Potable System
Drinking-water use is where a simple rain-barrel project becomes a water-treatment project.
Before relying on asphalt-roof runoff for potable use:
- Check local rules. Potable rainwater requirements vary by state and local jurisdiction.
- Identify the exact roofing and flashing materials.
- Determine whether the catchment materials are suitable for potable rainwater collection.
- Use debris exclusion and appropriate first-flush management.
- Use a covered, suitable storage tank.
- Design treatment around expected microbial and chemical hazards.
- Prevent cross-connections with the normal potable plumbing system.
- Have the treated water tested by an appropriate laboratory.
- Maintain the treatment system on an ongoing schedule.
EPA research treats roof-collected rainwater as a source that may require treatment appropriate to its intended use rather than assuming that roof runoff is inherently clean.
For potable systems, work with your local health authority and, when needed, a qualified water-treatment or plumbing professional.
The Bottom Line
An asphalt shingle roof can be used to collect rainwater, especially for lower-contact, non-potable uses such as ornamental irrigation.
The important point is that roof runoff is not the same as clean rain falling directly from the sky. Once water touches the roof, its quality depends on the shingles, flashing, gutters, surrounding environment, animals, storage tank, and maintenance of the entire system.
Use screens, keep the roof drainage system clean, consider first-flush diversion, and keep the tank protected.
For drinking or other higher-contact uses, do not rely on roof type or a single filter as proof of safety. Confirm the suitability of the catchment materials, provide treatment for the contaminants that may be present, test the finished water regularly, and follow current local health and plumbing requirements.
Frequently Asked Questions
Can I use rainwater from asphalt shingles in a rain barrel?
Yes. Asphalt-shingle roofs are commonly used to feed rain barrels intended for non-potable uses. Keep leaves and debris out, protect the barrel from animals and mosquitoes, and clean the system regularly.
Do asphalt shingles contaminate rainwater?
They can contribute substances to runoff, but the amount and type vary by roofing product and the rest of the system. Roof runoff can also become contaminated by dust, air pollution, bird droppings, flashing, gutters, and other materials.
Is a first-flush diverter necessary with asphalt shingles?
It is a useful water-quality control. A first-flush diverter sends the first, often dirtier portion of roof runoff away from the storage tank. It reduces contamination but does not make the water potable by itself.
Can I water vegetables with rainwater from an asphalt roof?
Use caution. Roof runoff can contain microorganisms and chemicals, regardless of roofing material. CDC guidance recommends using treated public or bottled water when possible for plants intended for eating. Check local health or agricultural guidance if you plan to use roof water on food crops.
Can a carbon filter make asphalt-roof rainwater drinkable?
Not by itself. Carbon filters address only certain contaminants and do not provide complete protection against all microorganisms or chemicals. Potable rainwater requires a treatment system designed around the actual water quality, along with regular laboratory testing.
Is rainwater from an old asphalt roof safer than rainwater from a new roof?
Roof age alone cannot establish safety. Shingle formulation, roof condition, flashing, repairs, coatings, debris, surrounding pollution, and maintenance can all affect runoff quality.
Should I collect rainwater after my roof has been chemically cleaned?
Do not send chemically contaminated runoff directly into your storage tank. Follow the cleaning product manufacturer's instructions and determine whether the roof is suitable for collection again before reconnecting the system.
