Distilled water has the advantage of being completely pure – but what does that mean for its shelf life? How long does distilled water last, and can it go bad? How do you know if distilled water is bad?
We’ve combined our knowledge and experience in the water treatment industry with our research into the science behind distilled water to answer all these questions and more.
📌 Key Takeaways:
- Distilled water can expire, although it’s less likely to go bad compared to normal tap water.
- Dust, airborne particles, contaminants from a dirty container, or the container materials may cause distilled water to go bad.
- Expired distilled water may have an unpleasant or unusual taste or smell, and its appearance may have changed.
Table of Contents
⚗️ Does Distilled Water Go Bad?
So, can distilled water go bad?
Yes, like any water type, distilled water can go bad. However, distilled water is far less likely to go bad than normal tap water because it has been treated with a purification process known as distillation, which removes all contaminants, impurities, and microorganisms, meaning that there’s nothing in the water that could cause it to go bad.
With that said, distilled water can still go bad if it’s affected by outside factors, such as poor-quality packaging or storage solutions, or pollutants from the environment. We’ve discussed these factors in more detail later.
📉 What’s The Shelf Life of Distilled Water?
The shelf life of unopened distilled water is indefinite. The manufacturer might advise a best-before date around 3-5 years into the future, but as long as the water is stored correctly in sealed bottles, it should last for years and years without going bad.
As we mentioned, distilled water doesn’t spoil or go bad in the traditional sense because it lacks the impurities that can support microbial growth or contamination. As long as the water remains in a clean, food-grade container and is protected from contamination, it can be stored for an extended period without compromising its quality or safety.
The shelf life of opened distilled water is 12 months, as long as the water is stored properly in glass bottles with lids. Ideally, store the water in your refrigerator or in a cool, dry place that doesn’t have access to excess heat, humidity, or direct sunlight. Make sure the container that you use is high-quality and won’t degrade – we always use glass bottles for this reason – and has a lid to prevent airborne contaminants from polluting the water.
🤔 What Could Cause Distilled Water To Go Bad?
There are a few different environmental factors that could cause distilled water to go bad, including:
- Exposure to dust or airborne particles
- Contamination from the materials in the storage container (such as microplastics or BPA from a plastic container)
- Airborne contamination that enters the water through a damaged container
- Exposure to heat or direct sunlight, which will cause certain containers to degrade and contaminate the water
To reiterate, if it’s stored properly in a sealed container, distilled water shouldn’t go bad. But poor storage practices may cause the water to go bad.
🔎 How Can You Tell if Distilled Water is Bad?
Left your distilled water open for a few weeks? Here are some of the signs to look out for that your water has gone bad:
Unusual Water Tastes
If you usually drink distilled water, you’ll know that it has a pretty bland, “flat” taste. When drinking distilled water that’s gone bad, you may notice unusual or unpleasant water tastes. The water may taste musty, or it may have a faint taste of the container it’s stored in (such as a plastic or metallic taste). This suggests that the water has been contaminated by the container materials.
An unpleasant smell is another sign that your distilled water has gone bad. Normally, distilled water doesn’t have a smell at all because it’s free from any odor-causing impurities or contaminants. But if the water goes bad or becomes contaminated, it could pick up an unpleasant odor.
Finally, if your distilled water has been contaminated with physical particles or pollutants, you may notice a change in its appearance. You may spot haziness or cloudiness (distilled water should normally always be clear), or you may see particles floating on the water’s surface. Some contaminants may even change the water’s color.
📆 How Long Can You Keep Distilled Water After Opening?
You can keep distilled water for up to 12 months after opening, depending on your purpose. For instance, if you’re drinking distilled water, you might not want to keep an opened bottle for as long as if you’re just using the water in your steam iron.
Just make sure to store the water in a suitable distilled water container with a lid. Avoid plastic containers where possible, since these can degrade over time and contaminate the water with chemicals and microplastics.
Technically, distilled water has no shelf life even after it has been opened, but we typically recommend 12 months to stay on the safe side, since there’s always a small risk of contamination once the water has been opened. Plus, the water will go stale after a few months, although you’re unlikely to notice a difference in taste because distilled water is pretty flat anyway.
Here are some of the estimates for how long distilled water should stay suitable for certain use cases after opening:
- Using in appliances and aquariums – 12 months
- Drinking – 1 week
- CPAP machines – 2-4 days
- Homemade distilled water – 5-7 days
📖 How To Keep Distilled Water Fresh
Let’s finish with a few of our top tips on how to keep distilled water fresh:
- Use a clean container. Our number one piece of advice is to store distilled water in a clean, food-grade container. Make sure the container is free from any debris or contaminants (give it a wash if you’re not sure!). Use a glass container for storing distilled water if possible.
- Seal the container tightly. Choose a container with a tight seal to keep the water safe and prevent contamination from dust, airborne particles, or other potential sources of impurities.
- Store the water in a cool, dark place. We also recommend that you store distilled water in a cool and dark location, away from direct sunlight, humidity, and heat sources. Light and heat can increase the risk of contamination from the storage container, so a dark cupboard or pantry is best.
- Practice good hygiene. This one is pretty obvious! Make sure you have clean hands when you’re handling distilled water, and avoid touching the inside of the container or the water itself. If you’re using any utensils for dispensing the water, ensure they’re also clean and sanitized.
- Rotate your stock. If you’re storing large batches of distilled bottled water, it’s good practice to use the oldest bottles first and replenish your stock regularly. That means you’ll always have a fresh supply on hand, and you won’t have to throw out old bottles at the back of your cupboard that you’d forgotten about.
📑 Final Word
We wrote this guide because we wanted to provide a clear answer to the question: “Does distilled water go bad?” We hope you’ve found it a useful resource if you drink distilled water or use it for other purposes (in your CPAP machine, steam iron, fish tank, etc.) and want to make sure you’re storing and using it safely.
Thankfully, the risk of drinking contaminated distilled water is very low. Just make sure to store distilled water properly, and, ideally, try to use it within 12 months of opening the bottle lid.
Can bacteria grow in distilled water?
Yes, bacteria can still grow in distilled water, even if the risk of bacterial contamination is lower than it is for normal tap water. For example, if the container used to store the distilled water isn’t properly cleaned and sanitized, it might introduce bacteria into the water. Another possible cause of bacterial contamination is if the water comes into contact with dirty surfaces or utensils.
Is it OK to drink expired distilled water?
Yes, it’s generally okay to drink store-bought distilled water that’s expired, as long as the water is stored in sealed bottles. Most distilled bottled water manufacturers label their bottles with a 3-5-year shelf life, but this is generally just guidance as distilled water can last indefinitely when it’s stored correctly.
How long does distilled water last for CPAP?
As we know, distilled water lasts indefinitely, but for a CPAP machine, it’s recommended that you use your distilled bottled water within 2-4 days after opening the bottle. Within this time period, the distilled water is at its highest quality and has a very low potential for contamination.
How long can water sit out distilled?
You can leave distilled or purified water to sit out for around 24 hours before using it for drinking, cooking, experiments, or use in household appliances. Storing distilled water is much better than leaving it sitting out because there’s a greatly reduced risk of contamination from airborne particles.