I had a question about some corrosion on my toilet water supply line. I've provided a picture below.

enter image description here

What I was wondering are a few things.

1) What is the reason for this? Why would a valve start building up corrosion while my other bathrooms do not.

2) Is it something I need to worry about and replace or can I just wash it with some solution to remove the corrosion or if I don't replace it will it cause a bigger issue down the line.

1 Answer 1


I cannot answer whether it needs replacing, but I can tell you why this happens.

It happens because it gets cold and water condenses on it.

Whenever you flush your toilet, cold water runs through and cools it off. Then the hot, humid air around it condenses water on it, making it moist. Because this happens so often, it will be moist a lot of the time, and thus corrodes.

Why this doesn't happen other places: The toilet is the one thing that uses most cold water. Your shower and sink uses more warm water, and not as much, and thus aren't as exposed to this phenomenon.

Unless it leaks I think you can leave it on.

  • +1 Some plumbers send tempered water to toilets, a mix of cold and hot. The tempering valve is set once and left, often in a basement or crawl space. It does require having both hot and cold available, and does use a very small amount of power (to heat the hot water), but totally eliminates warm weather sweating and this type of corrosion. A significant project best left to new work and renovations.
    – bib
    Aug 6, 2015 at 13:51
  • @kitalda Thank you, so is this normal and why do I not see it on all the toilets in my house, I'm assuming it just depends on the location? Would you advise I clean it off or just let it be?
    – Greenhoe
    Aug 6, 2015 at 14:31
  • Maybe: 1) It is the most used toilet in the house? 2) It is in the same room as the most used shower (more humidity in the air)? 3) The parts are made from a different material that corrodes more easily? 4) Some cleaning agent has been used there, but not at the other toilets, that started the corrosion? 5) Any combination of the above? If you can clean it off without damaging the part, sure, you can clean it, but if not, just let it be. If it gets worse (especially if rapidly) think about replacing it, but until then, no worries.
    – Kitalda
    Aug 7, 2015 at 6:40
  • Actually @bib has a point, that technique isn't used where I live (seen as wasteful), but that might be a reason it is the only toilet doing this. If You have tempered water in your toilets, but the tempering on this toilet is broken or off (too cold), it could be the explanation you are looking for.
    – Kitalda
    Aug 7, 2015 at 6:44

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.