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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 cooking.stackexchange.com/questions/24786/…
    – Amine
    Dec 13, 2012 at 17:18
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    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, 2012 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, 2015 at 21:22

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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 broadly safe.

She also said that she wouldn't do it under any circumstances. If the container is rusting so extensively you swallow sharp flakes of metal, you can die really horribly.

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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, 2013 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.
    – john_science
    Jan 24, 2014 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, 2014 at 19:33
  • just FYI, the body does not take in rust very well as a source of iron. Iron needs to be chelated in order for their to be a high degree of intake. Cooking in cast iron increases our iron level, but it does so over time through continuous exposure, not through dosing like drinking rusty water.
    – Escoce
    Mar 20, 2019 at 17:59
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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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  • Does that risk of tetanus apply when consuming water exposed to the rusty surface? I doubt tetanus would live in a bottle, but for example I wonder if a rusty nail falling in water would create a tetanus risk.
    – cr0
    Feb 15, 2019 at 16:59
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    @cr0: no. The association of tetanus with rusty metal is not because of the rust itself, but because the metal is good at cutting or puncturing, and rusty metal is often outside, dirty, and rough, providing a place for bacteria to live. They can also live just fine on unrusted stainless steel. Ingestion of Clostridium tetani carries virtually no risk, the bacteria and spores are everywhere to begin with, but it has to take up residence through a wound in an anearobic environment to produce the toxins.
    – whatsisname
    Feb 15, 2019 at 18:02
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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, 2014 at 21:02
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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, 2014 at 2:09
  • Welcome to outdoors.sx.com! 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, 2014 at 10:06
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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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