Prep first
Before you start
- Blot up standing water with a dry, white absorbent cloth or paper towels.
- Sweep off leaves and grit before you scrub so they don't get ground into the wood.
- Rinse the spot with a garden hose before you try anything stronger.
- Work out what the spot is first, since black growth, reddish-brown streaks and plain dark marks each need a different fix.
Water stains on a deck that have soaked into the wood itself are harder to lift than a surface mark. A surface spot usually responds to a rinse and gentle scrub, while black or gray mildew calls for an oxygen-bleach cleaner. If the wood has weathered to silver, its natural color may not fully come back, and those fibers should be left in place.
Rinse the area with a hose, then scrub gently with a soft brush along the grain of the boards. For a water stain on teak, try an oxygen bleach powder on a small patch first. Black or gray mildew on a wood deck calls for that powder, not a plain scrub.
Before you start
What decks & wood fences 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
Tap an item to get it on Amazon, or tick what you already have.
- Garden hoseFor the rinse before and after scrubbing.
- Mild dish detergentMixed in water for the first scrub. (opens Amazon)
- Stiff synthetic-bristle brushScrubs along the grain without metal. (opens Amazon)
- Oxygen-bleach deck cleanerTreats black or gray mildew. Follow the label's dwell time. (opens Amazon)
- Plastic drop clothCovers nearby plants during cleaning. (opens Amazon)
- Dry, white absorbent cloth or paper towelsBlots up standing water first. (opens Amazon)
As an Amazon Associate we earn from qualifying purchases.
5 steps
Step by step
Step 1 of 5
Clear debris and protect plants
Sweep away leaves and loose debris first. Cover nearby plants with a plastic drop cloth and spray them with water, which dilutes any overspray.
Step 2 of 5
Test in a hidden spot
Pick a hidden board or corner and try your cleaner there first. Do the same with any pressure washer setting before you use it on the visible boards.
Careful. Don't run a pressure washer on the visible boards until the test spot looks right.
Step 3 of 5
Rinse and scrub gently
Rinse the area with a garden hose, then scrub with mild dish detergent in water and a stiff synthetic-bristle brush. Work along the grain, not across it, so the scrubbing follows the lines of the wood.
Tip. Begin with light strokes and add pressure only if the spot doesn't lift.
Step 4 of 515 minutes
Treat mildew with oxygen bleach
If the spot is black or gray growth, apply an oxygen-bleach deck cleaner in sections so no area dries out. Keep it wet for the label's dwell time, about 15 minutes, misting with the hose if it starts to dry, then scrub along the grain. Skip this step if the spot is a plain water mark with no growth.
Careful. Don't let the cleaner or soap dry on the deck while it works.
Step 5 of 5
Rinse off all the cleaner
Rinse the whole area with the garden hose until no cleaner or suds remain, including the edges where it pooled. Let the deck dry fully before you judge the result.
Tip. A dry board shows its true color, so check the spot then rather than while it's wet.
If you'd rather buy than mix
Best products for water stains on decks & wood fences
Choose an oxygen-bleach deck cleaner, based on sodium percarbonate, and follow the dwell time on its label.
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 decks & wood fences, 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 cleaned board dries to an even color, with no pale ring or dark patch standing out. Mildew lightens noticeably after the oxygen-bleach step, and a dark mark that doesn't change after rinsing is in the wood itself, so it needs one of the set-in options.
What changes for yours
Adjust for your decks & wood fences
Cedar decking
Cedar is a soft wood, so the scrubbing needs to be lighter. Skip the pressure washer and caustic cleaners, since they can remove wood from the surface, and stick to the hose rinse and mild dish detergent with a brush along the grain.
If the spot is growth, the oxygen-bleach step still applies, but scrub it lightly and rinse it fully before you move on.
Wood deck
A wood deck needs no special changes to the cleaning. The one thing to watch is the pressure washer: use the lowest pressure that cleans, a fan tip, and spray with the grain.
If the spot is a dark mark that stays after cleaning, with no growth, the wood itself is holding the stain and you'll need the set-in options.
Composite decking
Composite boards vary by brand, so check the maker's care instructions before you use anything stronger than a rinse. If you can't find them, use only the hose and mild dish detergent with a soft brush.
Leave out the oxygen bleach, the oxalic-acid brightener and the pressure washer until you know the boards can take them.
Dark or black stains
Black spots may be mildew, so the oxygen-bleach step is the first thing to try, kept wet for about 15 minutes before you scrub along the grain. Dark marks that stay after that, with no growth, are old moisture in the wood itself.
Those usually need refinishing, which bleaches them out, rather than more scrubbing.
Heavy or long-standing buildup
If the spot is still there after the cleaning steps, the first question is how old it is. A white ring on finished wood that hasn't lifted after about five minutes of gentle buffing is probably too deep for mild methods, and the boards may need refinishing. Reddish-brown tannin bleed and rust streaks from nails need a different fix altogether.
For tannin or nail rust, use an oxalic-acid wood brightener exactly as its label says, after rinsing the oxygen cleaner off fully, since the acid neutralizes oxygen cleaners. Old stain or sealer comes off with a stain and sealer remover, which is neutralized with a brightener, and then the boards get a light sanding once they're dry. These are the strongest options, so don't reach for them before the gentle steps have failed.
A weathered, grayed deck can be restored with a commercial deck cleaner, brightener or restorer, which removes 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 rather than scrubbed harder. If the spot is still there after all of this, have a professional look at the boards before you go further.
Vinegar, baking soda, peroxide and more
Do home remedies work on water stains on decks & wood fences?
Most of the household remedies you'll find online don't belong on a deck, so only two are in the steps. Most of the others are a poor match for wood, and each has its own reason.
Works2Skip3Avoid1
What makes it worse
Mistakes to avoid
Don't use chlorine bleach on pressure-treated decks
Chlorine bleach breaks down the lignin in the wood, corrodes metal fasteners and harms plants nearby. It also doesn't kill mildew spores, so it fails at the job you'd be using it for.
Don't use narrow or rotating pressure-washer tips
Narrow-stream and rotating tornado tips are too concentrated for a deck. Stick to a fan tip, which spreads the spray across the boards.
Don't use steel wool or wire brushes on the boards
Leftover iron in the metal reacts with the wood's extractives and leaves dark stains. A stiff synthetic-bristle brush does the scrubbing without that risk.
Don't wet-clean an old CCA deck around kids or pets
Wetting raises the arsenic on the surface, and bleach releases chromate, so keep children and pets off wet CCA wood. If you can't tell whether the deck is CCA-treated, hold off on wet cleaning until you know.
When to call a professional
If the deck is old and may be CCA-treated, have it assessed before you wet it, and never cut or burn that lumber, since its sawdust and smoke contain arsenic. Old CCA lumber is best replaced rather than repaired. Pressure washers can damage a deck in the wrong hands, so hire a professional if you're unsure how hard to wash.
Questions
How do I prevent water stains on teak?
Blot standing water quickly with a dry, white cloth or paper towels, since a spot left wet is more likely to mark the wood. Rinse the deck with a garden hose regularly so grit and mildew don't build up on the boards.
Is oxygen bleach safe for a wood deck?
Yes, when you use it as directed, and it's the recommended option for mildew on wood. Keep it wet for the label's dwell time, about 15 minutes, then rinse it off fully.
How do I clean a weathered, gray deck?
Use a commercial deck cleaner, brightener or restorer, which removes 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 alone.
What's the difference between black spots and dark stains?
Black spots are often mildew, which the oxygen-bleach cleaner treats. Dark marks that stay after that, with no growth, are old moisture inside the wood and need refinishing rather than more scrubbing.
Does composite decking need the same steps?
Not exactly. Composite boards vary by brand, so check the maker's care instructions and start with only the hose rinse and mild dish detergent until you know what they can take.
Do I need to sand the deck after cleaning?
Not usually. Light sanding is for old stain or sealer after it has been removed and neutralized, or for tannin and rust areas after the brightener, and only once the deck is fully dry.
Water Stains on other materials
Other stains on decks & wood fences
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.