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I've got a thermos for coffee and/or water storage that I use on hikes and for bike touring since it keeps things hot for hours. However, it seems like the inside is rusting a bit.

Is this safe to use as is? Is this easily remedied, and how can I protect it from rusting again?

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I found this… – Amine Dec 13 '12 at 17:18
I was able to use a lot of baking soda, a little water, and a very sturdy bottle brush to get the inside of my thermos sparkling clean. It took a bit of work, but it got the job done. – Benzo Dec 18 '12 at 13:59
I have probably the same type of thermos that is made from food grade stainless steel, but still rusts a bit. I use it anyway. – alanh Jan 26 '15 at 21:22
up vote 9 down vote accepted

Warning! I am not a medical professional.

However, I asked my favorite doctor and she seemed to think it would be okay.

She said rust would just look like iron to your body and it would be consumed like food. So, I guess it is safe.

(Nota bene, if the container is rusting so extensively you swallow sharp flakes of metal, that is bad. The Chinese used to assassinate people that way.)

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The problem isn't the rust per-se, it's any other thing mixed in with the iron that may be released as it oxidises that's the problem. Whether there's likely to be anything else I couldn't say, but I still stand by my original answer in that it's not a risk worth taking when it can be cleaned with a bit of effort. – berry120 Jan 8 '13 at 0:46
@berry120 I wouldn't risk it on any normal day. But based on what Dr. Wife told me, I guess it would be safe and I would do it in a more emergency/dire situation. – theJollySin Jan 24 '14 at 18:24
Sure - though in an emergency a lot of normal rules would go out the window! I was more aiming at for general use. – berry120 Jan 24 '14 at 19:33

People do not realize that their public water are delivered by iron pipes buried 20 to 80 years ago. I was an engineering student and if you cut those pipes you will see rust around the pipes. So people do not realized that they are drinking water through rusted interior of water pipes. No one has died from it.

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Rust is not harmful to consume in either form (red or black) Black rust is magnetite and is what makes cast iron cookware black.

What is dangerous is being cut by something rusty, and danger has nothing to do with the rust itself. It is simply a great place for tetanus bacteria to live.

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I'd be wary of drinking from anything rusty personally - I'm not aware of the type of metal your thermos is made from, but several can start to produce potentially poisonous chemicals when they begin to oxidise. Sure, you could be ok but I wouldn't say it's worth the risk.

In terms of cleaning it, try something like Zud cleanser (readily available in the UK, not sure about other parts of the world.) Does a really good job at removing rust on anything I've tried it with!

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Can you say what type of metal produces poisonous chemicals when oxidized, and what those poisonous chemicals are? – shimizu Dec 16 '14 at 21:02

Put dish wash powder in and fill with hot water it will fizz let sit over night (don't put cap on gases will blow it off) was out it will look like new.

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It might oxidiz with liquids it's probably time to get a new one. – user2907 Jan 31 '14 at 2:09
Welcome to! Your answer is about cleaning thermos but the question was about if it is safe to drink from a rusty one, so it doesn't really fit and is likely to be deleted. Please have a look on our tour page to get some more information about the site and the Q&A format. – Benedikt Bauer Jan 31 '14 at 10:06

It's harmless. Rinse out anything loose. If you want, add a handfull of gravel, a cup of water, and shake for 10 minutes to get stuff out.

A thermos is going to be food grade metal. So the alloys will not be exotic ones with chromium or vanadium in quantity.

In passing: a 1 or 2 liter bottle with a pair of heavy socks pulled over it works nicely as a cheap thermos. I've used this for coffee on all day orienteering in winter, and even by day's end the coffee is at least warm.

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