How to Store Distilled Water: Keeping It Pure and Fresh

You have invested in quality distilled water for your CPAP machine, steam iron, or other applications. But how you store that water matters almost as much as your initial purchase. Improper storage can compromise purity, introduce contaminants, and reduce the effectiveness of distilled water for its intended purpose. This guide covers everything you need to know about storing distilled water correctly.

Understanding What Makes Distilled Water Pure

Distilled water's value lies in what it lacks: minerals, dissolved solids, and contaminants present in tap water. This purity makes it ideal for sensitive applications but also makes it vulnerable to contamination from external sources. Unlike tap water, which already contains various substances, distilled water readily absorbs anything it contacts.

When exposed to air, distilled water absorbs carbon dioxide, becoming slightly acidic over time. Contact with unclean surfaces introduces bacteria and other microorganisms. Exposure to certain plastics or containers can leach chemicals into the water. Proper storage minimises these contamination pathways.

The good news is that maintaining distilled water purity is straightforward with basic precautions. Understanding the risks helps you implement simple practices that preserve water quality from purchase to use.

Choosing the Right Storage Container

The original container your distilled water came in is typically the best storage option. These containers are designed for the purpose and made from food-safe plastics that will not leach harmful substances into the water. Keep water in its original container whenever possible.

If you need to transfer water to a different container, choose containers made from high-density polyethylene (HDPE), polypropylene (PP), or glass. These materials are chemically stable and will not contaminate distilled water. Look for recycling codes 2 or 5 on plastic containers, indicating HDPE and PP respectively.

Avoid storing distilled water in containers that previously held other substances, even after washing. Residues from soaps, foods, or chemicals can persist on container surfaces and contaminate your water. Purchase new containers specifically for distilled water storage if you need alternatives to original packaging.

Glass containers offer excellent chemical stability but present breakage risks and can be heavy when filled. They are excellent choices for countertop storage of smaller quantities but less practical for bulk storage.

Optimal Storage Location

Store distilled water in a cool, dark location away from direct sunlight. Heat accelerates potential chemical reactions between water and container materials, while light can promote algae growth if any biological contamination occurs. A cupboard, pantry, or storage closet typically provides ideal conditions.

Avoid storing distilled water near chemicals, cleaning products, or anything with strong odours. Plastic containers, while safe, can allow slow absorption of airborne chemicals or fragrances. This contamination may not be visible but can affect water quality for sensitive applications.

Keep water away from fuel storage, paint supplies, and garden chemicals. Australian garages, while convenient for storage, often contain automotive fluids and garden products that create unsuitable storage environments. Indoor storage is preferable for water intended for medical or food-related applications.

Temperature stability matters more than absolute temperature. Avoid locations with extreme temperature swings, such as outdoor sheds or uninsulated spaces. Freezing will not damage distilled water chemically but can rupture containers. Repeated freeze-thaw cycles stress container seals and may introduce contamination.

Shelf Life Considerations

Unopened distilled water has an effectively indefinite shelf life when stored properly. The water itself does not spoil or degrade chemically. However, over very long periods, trace amounts of substances may leach from plastic containers, and container integrity may eventually fail.

Most manufacturers recommend using distilled water within one to two years of purchase for optimal quality. This timeframe accounts for potential container degradation rather than any change in the water itself. Check containers periodically for cracks, clouding, or other signs of deterioration.

Once opened, storage timeframes depend on intended use. For general household applications like steam irons or automotive use, opened containers remain suitable for several months when properly resealed and stored. For medical applications like CPAP machines or nebulisers, use opened water within one to two weeks to minimise contamination risk.

Write the opening date on containers to track how long they have been in use. This simple practice prevents guesswork and ensures you use water within appropriate timeframes for your application.

Preventing Contamination During Use

How you handle distilled water during use affects its ongoing purity. Never pour used water back into the original container, even if it appears clean. Water that has been in a humidifier, iron reservoir, or other device has been exposed to potential contamination sources and should be discarded.

Use clean, dry measuring cups or pour directly from the container rather than dipping other containers or implements into your distilled water supply. Any object inserted into the container introduces potential contaminants, even if it looks clean.

Reseal containers immediately after pouring. Minimising exposure time to open air reduces carbon dioxide absorption and prevents airborne particles from entering. Ensure caps are fully tightened to prevent slow evaporation and contamination ingress.

Consider keeping smaller working quantities in a separate container for daily use, refilling from your main supply as needed. This limits contamination exposure for your bulk supply while maintaining convenient access for regular applications.

Buying and Storage Strategy

For regular distilled water users, developing a purchasing and rotation strategy ensures you always have fresh supply available. Calculate your approximate monthly usage across all applications to determine appropriate purchase quantities.

Buying in bulk often provides better value, with larger containers costing less per litre than smaller bottles. However, only buy what you can use within a reasonable timeframe. A 20-litre container offers excellent value but takes months to use if your consumption is light.

Practice first-in, first-out rotation with your distilled water supply. Place new purchases behind existing stock so older containers are used first. This ensures no water sits in storage longer than necessary. Compare distilled water products to find the right sizes for your usage patterns.

For emergency preparedness, maintain a modest reserve of distilled water for essential equipment. CPAP users, for example, should keep enough distilled water on hand for at least two weeks of use to cover potential supply disruptions.