can distilled water go bad

2 min read 19-03-2025

Distilled water, prized for its purity, raises a common question: does it expire? The short answer is no, distilled water itself doesn't "go bad" in the way milk or juice does. However, its purity can be compromised over time, affecting its suitability for certain uses. This article explores the nuances of distilled water's shelf life and how to best maintain its quality.

Understanding Distillation and Purity

Distilled water undergoes a purification process that removes nearly all minerals, impurities, and contaminants. This process leaves behind exceptionally pure H₂O. This lack of nutrients prevents the growth of microorganisms that cause spoilage in other types of water. Therefore, distilled water won't develop mold, bacteria, or algae.

Does Distilled Water Expire? The Truth

While distilled water doesn't spoil, its quality can degrade over time. This degradation isn't due to bacterial growth, but rather the absorption of airborne contaminants. Over extended periods, especially if stored improperly, the water can absorb carbon dioxide from the atmosphere, slightly increasing its acidity. Additionally, the container itself might leach minute amounts of chemicals into the water.

How Purity Can Change Over Time

Absorption of Gases: As mentioned, CO2 from the air can dissolve into the water, slightly altering its pH. This change is typically insignificant for most applications.
Leaching from Container: The material of the storage container can impact the water's purity. Plastic containers, for instance, might release trace amounts of chemicals. Glass is generally considered a safer option for long-term storage.
Dust and Particles: If the container isn't properly sealed, dust and other airborne particles can contaminate the water.

How to Store Distilled Water for Optimal Quality

Proper storage is key to maintaining the purity of distilled water. Here are some best practices:

Use a Clean Container: Always use a thoroughly cleaned container. Glass is preferred over plastic, although food-grade plastic is generally acceptable for short-term storage.
Seal Tightly: Ensure the container is tightly sealed to prevent the entry of airborne contaminants.
Store in a Cool, Dark Place: Avoid storing the water in direct sunlight or extreme temperatures. A cool, dark cupboard is ideal.
Use Within a Reasonable Timeframe: Even with proper storage, it's best to use distilled water within a year or two for optimal quality. For critical applications like medical use, consider shorter timeframes.

When Should You Discard Distilled Water?

While there's no definitive expiration date, you should consider discarding distilled water if:

The container is damaged or compromised: If the seal is broken or the container is cracked, discard the water.
The water is cloudy or discolored: This is a clear sign of contamination.
You notice an unusual odor: Any unusual smell indicates potential contamination.
It's been stored for an extended period (more than 2 years): While not necessarily harmful, the quality will likely have deteriorated.

Distilled Water for Different Uses

The acceptable level of degradation varies depending on the intended use of the water. For instance:

Ironing: Slightly less pure water is acceptable for ironing.
Car Batteries: Purity is less critical here than for other applications.
Aquariums: Use only distilled water that has been treated with appropriate additives for aquariums.
Medical or Scientific Applications: These uses demand the highest level of purity, and water should be used within a short timeframe after opening the container.

Distilled water, while not subject to microbial spoilage, can absorb contaminants over time. Proper storage and awareness of potential degradation are key to maintaining its quality and suitability for your intended use. If you have doubts about the purity, err on the side of caution and discard the water.