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When cleaning the faucet aerator I find the rubber washer gives off black stains as if it's dissolving. Does this mean it's time to replace the washer?

It also happened when replacing the faucet. There were rubber washers in the flex pipes that lead into the faucet. It felt like I opened a fresh black paint as my towel would not stop being stained.

I am concerned about this rubber dissolving and contaminating the drinking water.

Could someone shed some light if I'm missing something important about washer maintenance?

Dirty Towels

Supply Line

Aerator

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  • What are you using to clean the washers? Plain water should be good enough, maybe a small bit of soap. If the dye is coming off would blame the cleaner(chemicals). Would replace the washers.
    – crip659
    Jul 16, 2022 at 22:59
  • Well my hand turns black as soon as I unscrew the aerator or water connection. Attempting to dry with a paper towel takes a while it get it to stop bleeding. Worse, I cant seem to remove the washers from the water connections for replacing. Jul 16, 2022 at 23:01
  • In that case would say they are defective. I doubt if it is dangerous to drink. Do not think I have noticed any washer bleed dye before, have seen them get dry and cumber, if they are old ones.
    – crip659
    Jul 16, 2022 at 23:10
  • No we replace them when they leak. I would be less concerned about a tiny amount of rubber from a faucet seat than all the other contaminants in water like lead & fecal chloroform as 2 of the leading contaminates. Yes they do breakdown over the years if you are concerned swap them out. If your home was built prior to the mis 70’s lead solder was common in copper systems and community water systems still have high lead levels in Michigan and old towns that have not had the water mains replaced.
    – Ed Beal
    Jul 17, 2022 at 2:19
  • Yes, regularly or use the orange color one, that have more silicon in it, will not stain.
    – Traveler
    Jul 17, 2022 at 4:32

2 Answers 2

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I've definitely had them do that when they are old.

Generally plumbers replace supply lines when doing any work. Given the price of the supplies lines, the potential cost of a leak and the general cost of a plumber's labor, it doesn't make sense to re-use them.

I typically don't worry about it (unless the supply is plastic) but if I have a spare I'll swap it otherwise just re-use. All the water supply pieces are rated as safe for potable water and the washers are generally there to stop leaks ( they don't have a constant stream of water passing over them ). If the water was constantly passing over the washers there would be nothing to rub off on your fingers.

As long as there is no leak I don't think it is worth putting too much mental anguish into the state of the washer. If you live in a brand new perfectly finished home then replace the supplies pipes / plan to replace the supply pipes when doing a project and you know they are old. The cost is negligible compared to repairing any water damage unless your bathroom / kitchen already has some amount of water damage.

I did have a plastic cut to size toilet supply crack and cause a flood so if I ever see those I replace them immediately. Not sure what the best practice would be around braided lines with washers.

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  • It does not really answer the question. Do rubber washers dissolve and why?
    – Traveler
    Jul 17, 2022 at 2:54
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    Degradation of elastomer gaskets in contact with tap water may be caused by chlorine or chloramine (compounds of ammonia and chlorine) used to disinfect almost all water supplied by cities. Jul 17, 2022 at 2:58
  • thank you for clarifying
    – Traveler
    Jul 17, 2022 at 4:38
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    When the water is turned on for the first time after a shut off it's usually stained black from the washers, which is where my concern with water contact came into play. Jul 17, 2022 at 18:37
  • @CausingUnderflowsEverywhere with the large amount of staining you are seeing, I wonder if something larger than just little washers is involved. The flexible supply hoses leading out of shutoff valves have an elastomeric lining inside the hose that might be made of natural rubber in some of your lines. Also, the inner flexible bladder of any expansion tank may be made of rubber. Finally, after a shutoff you might be seeing water colored from e.g. sediment that is now being stirred up and flushed out. This last is what we see in our old galvanized water pipes in that case.
    – Armand
    Jul 17, 2022 at 20:25
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As FreshCodemonger noted, rubber gaskets and other items in contact with tap water will eventually weaken and disintegrate. The black stuff you see is likely carbon black being released as the rubber degrades. From The effect of carbon black composition in natural rubber compound

Almost all [natural] rubber compounds use carbon black (CB) as a filler. Carbon black filler functions to strengthen, increase the volume, improve the physical properties of rubber, and strengthen vulcanization.

Possible health hazards seem to be confined to breathing in (dry) carbon black into your lungs, or having it catch fire, neither of which seem to be relevant to washers disintegrating in water.

In my opinion, having the black pigment-like substance released indicates significant degradation has already happened and so the washer or hose should be replaced.

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  • @Ruskes Yes; I edited answer to clarify that it is the natural rubber compounds that typically have carbon black added to them.
    – Armand
    Jul 17, 2022 at 13:02

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