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Can Distilled Water Go Bad?

Even though distilled water isn’t usually meant for drinking purposes, I think it still makes perfect sense to cover it on the website. Many people, especially first time buyers, don’t quite know how to go about storing such water and how long they can keep it around before discarding. Because of that, I prepared this article, in which we go through storage, shelf life, and going bad of distilled water.

Please note that the advice in this article is meant for anyone using distilled water for household appliances and motor industry related work (e.g., refilling electrolytes in a battery). It’s by no means exhaustive for medical purposes. And in case you wondered if drinking distilled water is safe, the long story short is drinking some won’t do you any harm, but switching to drinking only distilled water is not recommended and probably a bad idea ([DWC-SA]). Having cleared that up, let’s get started.

Steam iron
(credit: Filip Mroz )

Can Distilled Water Go Bad? How To Tell If Distilled Water Is Bad?

Technically speaking, it’s difficult to tell what a “spoiled” or “bad” distilled water exactly is. If it’s water that has some impurities, then sure, just open the container and leave it unsealed for a few hours. Chances some dust, bacteria, or anything else will get into the container are very high. And no, you won’t be able to tell that it has any possible contaminants just by looking at it. Fortunately enough, if you’re using the distilled water, or any other type of purified water, for your home appliances, that liquid doesn’t have to be 100% to do its job. That water is still much “cleaner” than tap or bottled water, and good enough for your purposes.

Once you open the container and store it for a very long time (think months), chances are green algae will start to grow in there. Chances of that happening are much higher if your storage practices aren’t that great (more on that later). If the algae got to the point that there’s visible sediment in the bottle, it’s time to discard it and get a new one. Same thing if the water develops an off smell. But to check that, please pour some of the distilled water in a glass and only then take a sniff. This way you don’t smell the container, but only the water.

How Long Does Distilled Water Last?

In short, it depends. As long as the container or jug is unopened, it should easily last years. If it comes with an expiration date on the label, that’s a decent place to start. Usually, it’s between 3 to 5 years from the production date. Of course, a couple of months past that date the water should be still perfectly fine.

How long does opened distilled water last, you ask? Depends on how you plan to use it. If for any reason you need it for drinking purposes, I’d go about it as if it was bottled water. That means you probably should finish the bottle within a couple of days, a week tops. But if you’re using the distilled water for any home or garage appliances, it should easily last 9-12 months after opening in good shape. And it shouldn’t come as a surprise that proper storage methods help with keeping the distilled water pure.

Busy craftsman in a toolshed
(credit: Clark Young)

How To Store Distilled Water?

Distilled water is best stored in glass ([DWC-ST]), so if you’re using your own container, use a glass one. Plastic containers often leach a trace amount of chemicals to the water over time, and as you might imagine, that’s less than optimal. An excellent alternative to “normal” plastic ones are high-density polyethylene (HDPE) tanks and containers ([DWC-SL]), and many companies selling distilled water use those. The longer you plan on storing the distilled water, the more important the container is. So if you’re thinking about a long-term solution, go with glass of HDPE containers. A “normal” plastic bottle should be alright for short term storage.

When it comes to storing distilled water, there are a few practices you should follow. First, it’s essential to always keep the container sealed after opening, for obvious reasons. Second, keep the water in a dark place to prevent algae growth ([DWC-ST]). Third, avoid warm areas, as it’s easier for bacteria to grow in warmer conditions. That’s about it, really.

In a Nutshell

  • Unopened distilled waters last usually between 3 to 5 years. Check the label for details.
  • If you plan on drinking the water, finish it within 5 to 7 days. If it’s going to be used in various appliances, it should last at least a year if stored properly.
  • Store distilled water in glass or HDPE containers for best results. Plastic tends to leach a tiny amount of chemicals into the water.
  • Always keep the container sealed, away from light, and in a relatively cool temperature.