Why is the tap water yellow?

I have a complex and relatively unhealthy relationship with plumbing. I understand most of the basic concepts of plumbing, and have successfully replaced “modern” plumbing fixtures myself, however, my house is 107 years old, and when pipes and fittings are that old, that corroded, and haven’t moved in a hundred or so years, they get a little more difficult to deal with. Often, I simply don’t have the physical strength to get the old pieces off. I’ve learned that its best for my mental health to simply hire a plumber…

So, given that, whenever receiving an email from my tenants having anything to do with water, panic sets in (plumbers can be expensive, especially in an old house.) Tonight I received one with the foreboding subject line “water troubles.”

Apparently when they turned on the water, it was yellowish. They let the water run for a while, and it remained yellow. They weren’t sure if it was the plumbing in the house, or the city water lines, but they were relatively concerned about it and wanted to let me know.

Funny, when I got home tonight I ran some water for my plants and said to myself “huh, that water is yellowish.” knowing that it’s just something that happens with the city water from time to time, and it goes away.

So, lucky for me, it was just the city water, and it did go away. But why exactly does the water turn yellow sometimes?

I was always told it was just some rust in the water mains, they were flushing something or other out, or a fire hydrant was turned on somewhere. Out of curiosity, I did a little internet search to see if this was actually the case. According to the good city of Milwaukee WI):

The water at only one faucet appears rust-colored The corrosion of iron pipes causes water to appear rusty, yellow or brown colored. Because the discoloration occurs at only one tap, it is an indication of possible internal plumbing problems, not the city water supply. Call a plumber.

The water at all of the faucets appears rust-colored
The corrosion of iron pipes causes water to appear rusty, yellow or brown colored. If you see the color at all of the faucets, it is coming from the water main feeding your building. Run all of the cold water taps until the water runs clear, up to 10 minutes. If the problem persists, call the Milwaukee Water Works 24-hour Control Center…

Rusty water can stain laundry so avoid washing laundry, particularly white items, until the water clears. If you see rust stains on your laundry, you may want to try a product such as “Iron-out,” found in the laundry detergent section of stores. If the rusty water is an ongoing problem, call the Milwaukee Water Works Water Quality Section during regular business hours…

Milwaukee is much better known for their beer than their water, though, and they didn’t really say whyAlameda County Water District, in Fremont, CA:

Brown or yellow water from either tap on the FIRST DRAW:
The internal plumbing of your house is probably the culprit if discolored water only appears for a minute or two after your tap is turned on. When the zinc coating on the inside of galvanized iron pipe begins to wear thin, water becomes discolored as it comes in contact with bare iron. The longer the water sits in the pipes, the worse the discoloration will be. That’s why you are most likely to notice the problem first thing in the morning or when you have just returned from school or work. After running your tap for a few minutes, clean water from your water heater or water main will replace the discolored water. Since iron is an essential nutrient, this condition poses no health hazard. If the discoloration bothers you, however, flush the tap until the water becomes clear, saving the water for iron-loving plants.

Brown or yellow water from either tap, CONSTANTLY:
Sediments in water mains sometimes get stirred up when fire hydrants are used and when the flow of water in mains is reversed. These sediments may cause your water to turn brown or yellow. Thirty to forty minutes after you notice the discolored water, try turning on the cold water in your bathtub for a minute or two. You’ll probably notice that it clears right up, since sediments settle quickly back to the bottom of water mains. Discolored water due to sediments such as these poses no health threat, but for aesthetic reasons you should avoid doing laundry until the water clears up.

So, basically, the same “don’t freak out” message, and a little more explanation – it’s from the flow of water in the mains being reversed, or a fire hydrant being used.

I was able to send a very informative/know-it-all-ish email to my tenants, explaining what had happened, and that it seemed to have resolved itself after an hour or so. If only all plumbing problems were this easy to fix!

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