Does Water In A Thermos Go Bad?

Thermoses are known for their outstanding capabilities in storing water and food for later usage. However, you may have asked, “How long can water be stored in a thermos, and when should I throw it out?” This is a very common question amongst thermos users and a good one too! Does water in a thermos go bad?

You can keep water in a thermos for one day if you drink the water daily. It is advised that you throw out any water at the end of the day and wash your thermos to prevent molds and bacteria, especially if you’re taking it outdoors. Water can be stored for a week if a thermos is a high quality.

Are you worried that the water in your thermos bottle has gone bad? Whether you are wondering if you can store the water in your thermos overnight, for a week, or more, you will find everything you’re looking for in this article!

How Long Can Water Be Stored In A Thermos?

Generally, you will still be able to drink the water stored in a thermos the next day if it has been boiled.

However, it is not advised that you drink the water from a thermos on the third day because although the high temperature has sterilized the boiling water inside the thermos, the water in the thermos will still have been in contact with air during the drinking process.

A large number of microorganisms can be produced in only two days, which is easy to produce harmful substances, such as nitrite.

Therefore, it is not advised that you drink water from your thermos more than three days later.

Furthermore, no matter how good the heat preservation effect of your thermos is, the water will have cooled entirely down after three days of storage, so there is no need to use it for your coffee or any hot beverage anyways.

If you can boil another pot of water, it is recommended that you dispose of the old water and oil a new batch.

You can get very sick from consuming old water if it has been stored incorrectly. An open container or a thermos whose lid has been opened repeatedly can harbor several kinds of molds, insects, and bacteria.

It can also be contaminated with microscopic particles and dust.

If you decide to consume water in this condition, it could cause vomiting, diarrhea, as well as other serious complications.

However, there could be an exception to the three-day rule. If you plan on storing your thermos bottle properly, it could hold the water very well, and it can safely be consumed for roughly a week.

One-week-old water can still be safe for consumption as long as the thermos bottle is sealed correctly and clean.

Furthermore, the thermos bottle should also be stored in an area without direct sunlight. You will also be able to keep water for up to six months if the thermos bottle is tightly sealed and gets no direct contact with oxygen.

When Is It Safe To Drink Water From A Thermos?

Many people rely on thermos bottles during the coldest of the winter or during the hottest summer months. The thermos could be handy during the winter when boiling water is placed inside of the thermos and kept hot for hours at a time. This could be very convenient, but only for a short period.

However, sometimes, the entire bottle of water is not consumed and may need to be finished the next day. Knowing when water is safe to drink, especially in a thermos bottle, is an essential part of being the owner of a thermos bottle.

It is perfectly safe to drink water left overnight if the thermos is closed and sealed correctly. If the bottle is clean and does not show any signs of bacteria or mold, you can still consume the water in a thermos bottle for about a week.

However, this is not the case if the water has been stored in an open glass or stainless steel thermos and should not be consumed the next day. Water should always be held either at room temperature or colder than room temperature.

The area in which it is stored should not get in contact with any direct sunlight, as it could cause leaching to some thermos bottles.

Always keep the water far away from poisonous chemicals in order to avoid chemical reactions. If you have boiled the water and poured it into your stainless steel thermos bottle, sealed and covered, you can drink it the next day.

This is because the microorganisms and bacteria are instantly killed after the tap water has been boiled. The bacteria and microorganisms will be unable to enter the thermos bottle when in its sealed state, so you can store it overnight.

However, if your stainless steel thermos bottle was not filled with boiling water and its lid has not been covered while it is stored, it is advised that you should not drink it the next day.

Also, if your thermos bottle’s sealing performance is not up to standards, it is also not recommended to consume the water the next day, even if you decide to boil it again.

Is It Safe To Drink Water From Thermos Bottles?

Thermos bottles are made of stainless steel, making them one of the safest types of reusable water bottles to drink from if they are of high quality.

Stainless steel is a non-toxic material and does not need a liner. It is a type of metal that doesn’t leach any chemicals. This means that even if your thermos bottle becomes damaged, or if you fill the bottle with boiling liquids, it won’t become unsafe to consume its contents.

Also, you can wash your thermos bottle at extremely high temperatures, so you run little to no risk of your water becoming contaminated with bacteria or mold.

Washing your reusable thermos bottle regularly with hot water and soap will effectively kill any bacteria, so rest assured that you are safe when drinking your water from your thermos!


Now that you know the water in your thermos can go bad, it takes out most of the guesswork! If you store your water in a thermos, it would be best to empty out any water at the end of every day.

However, now you also know there are exceptions to this rule when water could be stored for much longer if kept in the right circumstances.


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