Prep first
Before you start
- Work out what your siding is made of before you choose a cleaner.
- Hose the spot down with low-pressure spray before you scrub.
- Test any cleaner in an inconspicuous area first.
Water stains on siding are often a mix of dried deposits, dirt and sometimes mildew, and the fix depends on what the siding is made of. Vinyl, stucco, stone and wood each take cleaning differently, so the spot needs a gentle start. A black or dark streak may be mildew rather than a water mark, and that needs oxygen bleach rather than more scrubbing.
Rust streaks on vinyl siding need a different product than mildew, so test any cleaner on a hidden spot first. Wood siding can be marked by too much force, so keep a pressure washer well away from it. If the mark won't lift after a couple of gentle tries, stop and call a siding pro before you strip the finish.
Before you start
What siding, roof & exterior can take
Safe to use2
- Water
- Oxygen bleach
Use with care5
- Soaking
- Chlorine bleach
- Solvents (alcohol, spot removers)
- Acids (vinegar, lemon)
- Scrubbing and abrasives
6 items
What you'll need
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- Garden hoseFor the low-pressure rinse before and after scrubbing.
- Mild dish detergentMixed in water for the gentle wash. (opens Amazon)
- Soft brush or clothCleans the siding without damaging the surface; a cloth is the choice for fiber cement. (opens Amazon)
- Plastic drop clothProtects nearby plants from the cleaner and overspray. (opens Amazon)
- Oxygen-bleach cleanerTreats mildew or organic growth on the surface. (opens Amazon)
- Household bleachOnly for the dab test on vinyl or wood, never as a cleaner. (opens Amazon)
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5 steps
Step by step
Step 1 of 5
Clear debris and protect plants
Sweep away leaves and debris from around the spot before you start. Protect nearby plants with a plastic drop cloth, and spray them with water to dilute any overspray.
Step 2 of 5
Test cleaner and check for mildew
Test any cleaner, and any pressure washer setting, in an inconspicuous area first. If the spots are black and the siding isn't fiber cement, do the bleach dab test on a small spot to see whether it's mildew.
Step 3 of 5
Rinse and gently scrub the siding
Rinse the spot with a garden hose on low-pressure spray first. Then scrub with mild dish detergent in water and a soft brush. On fiber cement, use a soft brush or cloth.
Tip. Rinse one section before you scrub it, so you can see how the stain responds.
Step 4 of 515 minutes
Treat mildew with oxygen bleach
Apply an oxygen-bleach cleaner to one section at a time, and keep it wet for the label's dwell time, about 15 minutes. Mist it with a hose if it starts to dry, then scrub gently and move on to the next section. On fiber cement, use a mildew-specific cleaner and a soft cloth instead.
Step 5 of 5
Rinse everything off thoroughly
Rinse thoroughly with a hose, working over every section you cleaned until no suds are left. Once the siding is rinsed, let it dry before you look at the spot.
Tip. If the spot is still there once the siding is dry, check the card for your siding type below.
Careful. Don't let cleaner or soap dry on the siding; rinse each section before it dries.
If you'd rather buy than mix
Best products for water stains on siding, roof & exterior
Pick an oxygen-bleach cleaner labeled for mildew, and check its dwell time before you start. For fiber cement, choose a mildew-specific cleaner made for that material.
OxiClean Versatile Stain Remover Powder
How we picked these: each product is made for this type of stain, its maker doesn't warn against using it on siding, roof & exterior, and its directions fit the steps above.
Finished the steps? How does it look?
Nice work. Let it dry completely and check it again in good light. Here is what done looks like:
How to tell it's really gone →A faint mark usually needs one more round, not a stronger product.
Heavy buildup usually takes more than one round.
Heavy or long-standing buildup →When to call a professional →How to tell it's working
A clean spot matches the siding around it and dries evenly without a ring. If a black spot stays after the oxygen-bleach step, it's probably not mildew, so check the card for your siding type before using anything stronger.
What changes for yours
Adjust for your siding, roof & exterior
Water on vinyl siding
On vinyl siding, the oxygen-bleach step works, but keep the rest of your cleaning gentle. Don't use organic-solvent cleaners, undiluted chlorine bleach, liquid grease remover, nail polish remover or furniture polish, and don't aim a pressure washer upward.
Once the siding is dry, check the spot in daylight, since a faint mark can look worse when it's wet. Stains that have been there a while are covered by the set-in options.
Water on stucco or stone siding
For stucco and natural stone, keep the approach as gentle as possible. Stick to the hose rinse and the mild dish detergent wash, and test any cleaner in an inconspicuous area first.
If the spot doesn't lift with the gentle wash, stop there rather than moving on to stronger products on the wall.
Water on wood siding
On wood siding, the oxygen-bleach step handles mildew. For reddish-brown tannin bleed or rust streaks, use an oxalic-acid wood brightener per its label, after you've rinsed the oxygen cleaner off, since the brightener also neutralizes it.
If you pressure wash, use the lowest pressure that cleans, a fan tip, and spray with the grain. Don't use a narrow-stream or rotating tornado tip, and don't power wash softer woods like western redcedar, since it removes wood from the surface.
Heavy or long-standing buildup
Weathered, grayed wood can be restored with commercial deck cleaners, brighteners or restorers, which remove mildew and dirt so the wood's own color shows. If all of the natural color has leached out, the wood stays silver when dry, and those fibers should be left in place.
Old stain or sealer comes off with a stain and sealer remover, which you then neutralize and lightly sand once it's dry. Work in small areas and check each one before you move to the next, so you don't spread the stain.
A stain that's still there after these steps is often set into the wood itself, so aim for less visible rather than gone. Expect the set-in options to fade it, not erase it.
Vinegar, baking soda, peroxide and more
Do home remedies work on water stains on siding, roof & exterior?
Most household remedies don't suit siding; rinsing and gentle scrubbing handle most spots. Patch-test any product on an inconspicuous area first.
Works2Skip4
Chemical safety
Never mix these
Some products in this guide react dangerously with each other. Use them one at a time and rinse with water in between.
Chlorine bleach + Oxygen bleach (OxiClean)
Both makers advise against combining them: OxiClean says not to mix it with chlorine bleach, and Clorox says the two bleaches cancel each other out.
If they mix by accident: Don't use the mixture; ventilate the room and avoid breathing fumes or touching it; call Poison Control at 1-800-222-1222 for disposal advice or if anyone feels unwell.
What makes it worse
Mistakes to avoid
Don't power wash fiber cement siding
A high-pressure power washer can damage fiber cement siding and its finish. Never use bleach or acid on it, and avoid a hard metal brush or an abrasive sponge, since these can damage the surface. Stick to the hose, a soft brush or cloth, and a mildew-specific cleaner.
Don't use steel wool on wood siding
Steel wool and wire brushes leave iron behind, and the iron reacts with the wood and stains it. Use a stiff synthetic-bristle brush along the grain instead.
Don't mix bleach with ammonia
Never mix bleach with ammonia or a detergent containing ammonia, because the combination forms a toxic gas. Keep each cleaner separate and rinse fully before you use the next one.
When to call a professional
A professional is the safer call if the wall is large, the spot is high up, or the spot doesn't lift after the gentle steps. Pressure washers can damage siding in the wrong hands, so a pro with the right equipment is the better choice for those jobs.
Questions
Can I use vinegar on siding to remove water stains?
No. Vinegar isn't a recommended siding cleaner, and it's unsafe on natural stone, so keep it away from stucco or stone siding. It's also unsafe on natural stone, so keep it away from stucco or stone siding.
Is a dark ring on wood siding the same as a light one?
No. A white ring means moisture got into the finish, while a dark ring is old moisture in the wood itself. Dark rings in bare wood are bleached out as part of refinishing, so a cleaner alone won't fully remove them.
What if the spot is still there after cleaning?
Check it once the siding is dry, since wet siding can make a faint mark look worse. If it's still there, the set-in options cover older stains.
Can I use the bleach dab test on fiber cement?
No. Skip the dab test on fiber cement and use a mildew-specific cleaner with a soft cloth instead. The dab test is only for vinyl and wood siding.
Can I use hydrogen peroxide on rust-colored spots on vinyl siding?
No. Start with the gentle wash on rust-colored spots, and test any cleaner first. Peroxide isn't the answer for rust-colored spots on vinyl; mild washing is the safer choice.
Should I hire someone for stucco or stone siding?
Yes, if the spot doesn't lift after a gentle wash. A professional can handle anything that needs stronger products. Let a professional handle anything that needs stronger products.
Water Stains on other materials
Other stains on siding, roof & exterior
Start from the bigger picture
How we know this
Every method, amount and warning here comes from university extension services, industry bodies and product makers. We read them, check every step for unsafe combinations and changed amounts, and write it up so you can follow it.