How long can you keep purified drinking water?

November 25, 2025 •

4 min read

While pure water itself does not technically expire, its storage container can compromise its quality over time. A key factor is the type of container used, particularly plastic, which can degrade and leach chemicals, affecting taste and safety. Knowing how long you can keep purified drinking water depends heavily on proper storage practices.

Quick Summary

The lifespan of purified drinking water is determined by its container and storage conditions. Plastic can degrade, affecting taste and safety over time, while proper storage in cool, dark environments using food-grade materials is crucial for longevity and freshness. Signs of spoilage, including odor and taste changes, indicate water should be discarded.

Key Points

Water doesn't expire, but the container does: The "best by" date on bottled water relates to the plastic bottle's potential degradation, not the water itself.
Heat and light accelerate breakdown: Storing water bottles in a cool, dark place prevents chemicals from leaching out of the plastic and preserves water quality.
Opened water is susceptible to contamination: Once a bottle is opened, airborne bacteria can enter and grow, especially without chlorine to act as a disinfectant.
Reusable bottles need daily cleaning: Microbes from your mouth and hands can contaminate water in a reusable bottle, making it unsafe if left for more than a day or two.
Use glass or stainless steel for long-term storage: These materials are non-porous and won't leach chemicals, making them ideal for storing water for longer periods.
Discard if the water smells or tastes off: Any unusual odor, taste, or visible cloudiness is a sign of contamination, and the water should be thrown out immediately.
Rotate emergency water supplies: For optimal freshness and safety, rotate your stored water every one to two years, even if in sealed containers.

Understanding the Lifespan of Purified Water

Pure H2O is a stable compound that does not spoil in the same way that food does. The primary issue affecting the longevity of purified water is its exposure to the external environment, especially the storage container. Properly stored in a sealed, sanitized, food-grade container and kept away from heat and light, purified water can remain safe for drinking for an extended period, often years. However, once the container is opened, the risk of contamination from the air and handling increases significantly, and the shelf life drops dramatically.

Factors Influencing Purified Water's Shelf Life

Several elements dictate how long purified drinking water stays safe and fresh:

Container Material: The type of material used for storage is critical. Plastics, especially single-use PET bottles, are slightly permeable and can degrade over time, leaching chemicals like BPA into the water. Glass and stainless steel are non-porous and do not leach chemicals, making them ideal for long-term storage.
Storage Conditions: High temperatures and direct sunlight accelerate the breakdown of plastic containers and can promote the growth of microorganisms in the water. A cool, dark environment, like a pantry or basement, is best for maintaining water quality.
Container Seal: A tightly sealed container prevents airborne bacteria, dust, and other contaminants from entering the water. After opening, an airtight seal becomes especially important.
Original Purity: Purified water, whether through reverse osmosis, distillation, or other methods, is free of most contaminants and microorganisms at bottling. However, once opened, it lacks the residual chlorine found in tap water that inhibits bacterial growth.

Opened vs. Unopened Containers

The difference in shelf life between opened and unopened purified water is significant. An unopened, factory-sealed bottle stored correctly can remain safe to drink for years, though manufacturers often add a 'best by' date relating to the packaging rather than the water itself. Once opened, the water is exposed to the environment. Microbes from the air, or from direct contact like drinking from the bottle, can enter the water. For water from a dispenser or a large jug, it is generally recommended to consume it within a few days to a week.

Signs that Purified Water Has Gone Bad

Even with purified water, it's wise to be vigilant for signs of spoilage, which indicate potential contamination:

Off-putting Odor: Pure water should be odorless. A musty, moldy, or plasticky smell can indicate chemical leaching or microbial growth.
Unusual Taste: A stale, bitter, or chemical taste is a clear sign that the water's quality has degraded. Plastic leaching is a common cause of a metallic or plasticky flavor.
Visual Changes: Clear water should be just that—clear. Cloudiness, discoloration, or floating particles are red flags for bacterial or algae growth and should not be consumed.

Long-Term Storage for Purified Water

For emergency preparedness, storing purified water correctly is essential. Using large, food-grade containers made of high-density polyethylene (HDPE), glass, or stainless steel is recommended. Store these containers in a cool, dark location away from chemicals, pesticides, or other strong odors that plastic can absorb. Even with ideal conditions, it is a good practice to rotate your emergency water supply every one to two years.


Storage Scenario	Approximate Safe Duration	Critical Factors
Sealed Commercial Bottle	Years (beyond best-by date)	Proper storage away from heat and light, container integrity
Opened Dispenser/Jug	3-7 days	Exposure to air, temperature, handling hygiene
Refilled Reusable Bottle	1-2 days	Daily cleaning is essential; bacterial growth from mouth
Room Temperature in Glass	Up to 12 hours	Absorbs ambient odors, bacterial growth
Emergency Storage Container	1-5+ years	Use food-grade material, store in cool, dark place, rotation

The Difference Between Purified and Distilled Water

Purified water is treated to remove chemicals and contaminants, but may retain some beneficial minerals. Distilled water, a type of purified water created by boiling and recondensing the steam, removes almost all minerals and dissolved solids, resulting in a flatter taste. While distilled water has a higher initial purity, it is not necessarily superior for drinking, as the lack of minerals can be a drawback for some. Both, however, are subject to contamination if not stored properly.

Conclusion

While the chemical compound H2O is stable, the surrounding environment and container material are the key determinants of how long you can keep purified drinking water. The purity of the water is only as good as its storage. For daily use, finish opened water within a few days and keep reusable bottles clean. For emergency stocks, prioritize food-grade containers and store them in a cool, dark place, rotating them periodically. By understanding the science behind water storage, you can ensure your drinking water remains safe, fresh, and free from contaminants.

This article is for informational purposes. For health concerns, consult a medical professional.

Frequently Asked Questions

Yes, if the bottle is unopened and stored correctly in a cool, dark place, the water is likely safe to drink, as the expiration date primarily concerns the plastic packaging's integrity, not the water's spoilage. However, the taste may be affected over time.

Purified water in a dispenser should be consumed relatively quickly once the bottle is opened, typically within three to seven days. The constant entry of air bubbles increases the risk of bacterial contamination.

Yes, they are different, but their storage longevity is similar once opened. Distilled water is a type of purified water with almost all minerals removed, but both can be contaminated if not stored properly. Distilled water's ultra-purity may even leave it more susceptible to bacterial growth once exposed to air, as there's nothing left to inhibit it.

Use clean, food-grade containers made of durable plastic, glass, or stainless steel. Fill them completely and seal tightly. Store in a cool, dark place away from chemicals and sunlight. Rotate your stock annually for the best quality.

Glass and stainless steel are the best non-leaching options for long-term storage. For plastic, choose food-grade HDPE (marked with a #2 recycling symbol), as it is less permeable than other plastics.

Trust your senses. If the water has an unusual taste (plasticky, metallic), a strange odor (musty, foul), or any visible cloudiness or particles, it is no longer safe and should be discarded.

Yes, once exposed to air and handling, bacteria can enter purified water and multiply over time. Unlike chlorinated tap water, purified water lacks disinfectants, so it is more susceptible to bacterial growth after opening.