Hydro Flasks are great water bottles that can keep ice cold for 24+ hours and drinks hot for 12+ hours. But Hydro Flasks are made from metal, stainless steel metal, and metal has a tendency to rust over time – especially when exposed to water. So do Hydro Flask's rust?
If Hydro Flasks rust what is it that causes them to rust, what can you do to prevent rust and how can you clean rust from a Hydro Flask?
Hydro Flasks are made from 18/8 stainless steel which is rust-resistant, but it is possible for Hydro Flasks to rust.
What Makes Hydro Flasks Rust Resistant?
Hydro Flasks are made from stainless steel. You are likely aware that steel has a tendency to rust, especially when exposed to water and salt water.
So what is it that makes Hydro Flasks rust resistant? Is there something special about them?
Hydro Flasks are made from 18/8 Stainless Steel. That means they contain 18% chromium and 8% nickel. The chromium in the Hydro Flask is what makes it rust resistant.
When regular steel is exposed to water ferric oxide is created which has that red rust color.
However, when stainless steel is exposed to water chromium oxide is created. This forms a thin layer on the stainless steel which doesn't come off. This protects the underlying stainless steel from being exposed to more water and stops it rusting.
So there is no magic, or no plastic layer over the stainless steel on the inside of your Hydro Flask. It is simply the chromium in the stainless steel that makes it unlikely to rust.
As long as the chromium component is over 12% then it should be rust resistant. Given it's 18% in Hydro Flasks then your bottles should be unlikely to rust.
How Likely Is A Hydro Flask To Rust?
Hydro Flasks are rust-resistant and they are extremely unlikely to rust with regular usage. But it is definitely possible for Hydro Flasks to rust.
This reddit post is a perfect example of a bit of rust on the inside of a Hydro Flask:
There is also this customer review where they claim there is rust in the bottle after 2-3 months of usage.
Given how many millions of Hydro Flasks have been sold over the years and how few references I could find to Hydro Flasks rusting I would say it is highly unlikely for Hydro Flasks to rust, but definitely possible.
What Causes A Hydro Flask To Rust?
There are a variety of things that can cause the stainless steel in a Hydro Flask to begin to corrode and rust.
Corrosive Chemicals Like Bleach/Chlorine
Stainless steel is considered non-reactive to most food/drinks but corrosive chemicals and super acidic liquids like bleach and chlorine can cause the stainless steel to corrode and begin to rust.
Long Exposure To Salt Water
Salt water is more corrosive to stainless steel than regular water, so if your Hydro Flask has long exposures to salt water (eg. left outside and you live near the ocean) then it could cause some rusting.
The 18/8 stainless steel that Hydro Flasks are made from can withstand heats up to about 750-1550°F (400-850°C) without issues. But once you get up to these temperatures it can cause the surface of the stainless steel to no longer contain enough chromium to protect the bottle from rusting.
There are other more extreme reasons stainless steel can rust discussed here but they are highly unlikely to affect your Hydro Flask.
How To Prevent Rust in a Hydro Flask
Preventing rust in your Hydro Flask is pretty easy. You simply want to keep it away from corrosive liquids like bleach or salt water.
There are some questions about whether it is ok to put lemon in a Hydro Flask but it doesn't seem like this would cause it to rust.
You also want to make sure you're cleaning it on a regular basis and also leaving it to dry so extra moisture is not trapped in the bottle. Click here to learn how to clean a Hydro Flask properly.
How To Clean Rust From a Hydro Flask
Maybe you've accidentally exposed your Hydro Flask to a corrosive liquid of you're like this unfortunate person who's mother decided to soak their Hydro Flask in bleach for 2 days. How do you clean rust from a Hydro Flask?
What NOT To Do
There are a couple of things right off the bat that you DON'T want to do as this can cause more rust and other issues with your Hydro Flask.
Don't put your Hydro Flask in the dishwasher as it can break the Hydro Flask insulation (learn more)
Don't use bleach in your Hydro Flask as it'll cause more rust and corrosion to your Hydro Flask.
Don't use steel wool to clean your Hydro Flask. While this will remove the surface rust it can leave little flecks of steel on the inside of your Hydro Flask which over time can rust
So How Should You Clean Rust From a Hydro Flask?
There are a few different strategies you can use to clean rust from your Hydro Flask.
Use a Magic Eraser
Magic erasers are made from a type of plastic foam that happens to be micro-abrasive.
This makes it perfect for cleaning off rust but it won't leave behind flecks of steel that will in turn rust in the future.
Coca-cola is both acidic and it contains phosphoric acid. This dissolves the rust corrosion and you can then wipe most of it off with a bottle brush with tough bristles or with the magic eraser mentioned above.
Phosphoric Acid Liquid or Gel
If you want to go to the extreme then you can buy phosphoric acid or gel that you can use to remove the rust.
You should be able to get it as a rust remover from your local hardware store.
Using an abrasive cleaner like bicarb soda can help to remove the rust with a good scrub. Mix with vinegar as the acidic vinegar can also help.
Or get an abrasive sponge or bottle brush and use that to rub away the rust.
Fine Steel Wool
While I don't personally recommend using steel wool if you don't want to try anything else then you can use 0000 fine steel wool which will polish away the rust.
Just make sure you thoroughly clean your bottle afterward to remove any steel particles as these will likely cause future rust issues.
The good news is that once you've cleaned away the rust from your Hydro Flask the chromium should form a naturally protective layer and it shouldn't just rust again.
If your Hydro Flask continues to rust even after you've remove old rust then there may be a manufacturing defect and you may need to contact the company and ask for a replacement.
Does The Hydro Flask Warranty Cover Rust?
If you don't want to clean the rust from your Hydro Flask or you've tried to clean the rust without success you may be wondering does the Hydro Flask warranty cover rust?
There is nothing about rust on the Hydro Flask Warranty page so I did some digging to find out more.
Yes, the Hydro Flask warranty covers damage by rust. While their warranty page doesn't say this their Amazon posts to customers as well as customer testimonials show they will replace rusted Hydro Flasks.
This Hydro Flask Amazon customer asked here about if the limited lifetime warranty covered rust in the inside of the bottle because their friend's bottle had shown rust after just 4 months.
Wendy from Tall Ridge (Tall Ridge are the exclusive seller of Hydro Flask products on Amazon) said this:
“Yes, rust is not common but it is covered by the Hydro Flask warranty. I hope that helps!”
There's even a customer example of Hydro Flask honoring this warranty and replacing a rusted Hydro Flask.
This post by Jalna on her Blogspot blog back in 2015 shows the corrosion and rust on their old Hydro Flask and they talk about how it was replaced and all they had to pay was shipping!
It's great to see that yes the Hydro Flask warranty does cover rust.