Blue-Green Stains in the Sink and Tub
Blue-green stains are copper leaving your own pipes. Slightly acidic water dissolves a little copper as it sits in the plumbing, then deposits it on porcelain and fiberglass where water stands or drips, so the color is both a stain to clean and a sign worth reading.
The short answer
Make a paste of Bar Keepers Friend on the wet stain, let it sit briefly, and rub with a soft sponge before rinsing. It holds 4.8 stars from 2,118 reviews on Home Depot (November 2026), with 97 percent of reviewers recommending it. The same acid that lifts this stain also lifts rust marks and deposits on faucets, which is why one canister covers all of these metal stains.
Why does this happen?
Water that is even slightly acidic, common with well water, dissolves copper slowly from the inside of copper pipes, especially overnight when water sits still in contact with the metal. When that water runs into a sink or tub and evaporates or stands around a drain or drip line, the dissolved copper oxidises on the surface as a blue-green deposit. The color is the diagnostic: blue and green point to copper, while orange and brown point to iron and rust.
The stain itself is a surface deposit, so an acid that dissolves metal oxides can remove it without abrasive damage when it is used briefly and rinsed well. Oxalic acid does that chemical work, which is why a paste and a short dwell outperform hard scrubbing with a general cleaner. What cleaning cannot do is change the water. If the stains return quickly, the water is still leaching copper, and that ongoing corrosion is a water treatment and plumbing question, not a cleaning failure.
The fix, in order
The steps are ordered cheapest first. Stop at the one that solves it and skip the rest; the product is there only for where the free steps run out.
Free step
Read the color and find the water path first
Blue-green means copper, orange means iron, and each has a different source. Note where the stain sits: under a dripping faucet, around the drain, or along the waterline of a tub that drains slowly. Fix any steady drip and clear slow drainage, because standing water is what lays the deposit down.
The product step
Clean the deposit with Bar Keepers Friend
Wet the surface, sprinkle the powder to a thin paste, and let it sit briefly as the label directs. Rub gently with a soft sponge, working the stained ring rather than the whole fixture, then rinse completely. Repeat once on a heavy deposit rather than scrubbing harder or leaving the acid on longer.
The product for this step
Bar Keepers Friend
Free step
Rinse, dry, and check the finish in daylight
Acid cleaners keep working while any residue stays wet, so rinse thoroughly as part of the cleaning, not as an extra step afterwards. Dry the area and look at it in natural light. A shadow that remains after two rounds is usually a much older deposit in a worn finish, and further acid rounds trade finish for very little gain.
Habit step
Watch how fast the stain comes back
Note the date you cleaned and check the spot weekly. A stain that takes months to reappear is ordinary deposit from ordinary use. One that returns in weeks is telling you the water is actively leaching copper, which is the point to test the water and talk to a plumber about treatment.
The evidence, in tiers
Tier 1 · The method
Oxalic acid dissolving metal oxide deposits is the established chemistry behind this cleanser class, and the product label itself directs the test first, short contact, and thorough rinse method the ladder follows.
Tier 2 · This product
Bar Keepers Friend holds 4.8 stars from 2,118 reviews on Home Depot (November 2026), with 97 percent of reviewers recommending it.
We have not stained a tub for this guide. The paste, dwell, and rinse method follows the product label and the copper deposit mechanism described above.
Tier 3 · What owners report
Owners report the pattern the chemistry predicts: green rings and rust colored marks lifting in one or two rounds, the same canister getting used on faucet handles and shower doors, and disappointment only where stains sat for years in worn finishes or where the water kept depositing faster than any cleaning schedule could match.
The alternatives, conceded where they win
| Option | What it is | The honest verdict |
|---|---|---|
| Bar Keepers Friend powder | Oxalic acid cleanser for metal oxide stains | The pick: it dissolves the copper deposit chemically instead of relying on abrasion, and the same canister covers rust and faucet deposits. |
| Vinegar on a cloth | Mild household acid soak | Wins on price and on being already in the kitchen, and it can soften a light fresh deposit given a long soak; it loses on older, heavier staining, where its weaker acid needs hours and still leaves a shadow. |
| Abrasive scouring pads and powders | Mechanical removal of the deposit | Its only advantage is that it starts working right away. It can scratch porcelain, fiberglass, and fixture finishes, and leaves a dull patch that then holds dirt and stains faster than the original surface did. |
The honest price comparison
The honest comparison is a plumber visit to assess the water and the pipes, which costs real money before any treatment is fitted, against a single canister of cleanser that handles the visible stain today. Clean first, and let how fast the stain returns decide whether the larger job is worth paying for.
Where it falls short
The weaknesses below come from the product's own review record, the same record the recommendation rests on.
- It is an acid, so it demands the test spot, gloves, and rinse the label requires, and it is the wrong tool for natural stone and some damaged finishes.
- It removes the deposit, not the cause. Acidic water will leave the stain again, and if it returns quickly, the plumbing problem still needs fixing.
- Very old deposits in worn or etched finishes may only fade, because the stain sits in surface damage rather than on top of the finish.
The product, in short
Bar Keepers Friend
Questions people ask next
Why is my stain green in one sink and orange in another?
Different metals leave different colors. Green and blue point to copper from pipes or fittings, while orange and brown point to iron, usually from the water itself or a rusting part. The color tells you which source to look for before you clean.
Will the stain come back after I clean it?
It can, because cleaning removes the deposit while the water chemistry that made it is unchanged. Slow returns over months are normal. A stain back within a few weeks suggests actively corrosive water, which is worth a water test and a plumber conversation.
Is it safe on a fiberglass tub?
Generally yes when used as the label directs, briefly and with a soft sponge, but finishes vary and older fiberglass can be thin. Test a hidden area first, never use a stiff brush or scouring pad, and rinse the surface completely when you finish.
Can I use it with bleach for a stronger clean?
No. Never mix an acid cleaner with bleach or with any other cleaning product. Use one product at a time, rinse the surface thoroughly between products if you change approach, and keep the room ventilated while you work.
Home Depot product record for Bar Keepers Friend (November 2026) · Bar Keepers Friend product label directions and warnings
The Fix JournalCase 31Home Surfaces