Myth Debunked: Does Water Have No Expiry Date?

December 14, 2025 •

4 min read

While pure H2O is a chemically stable substance that does not spoil, many bottled water brands still feature a "best by" or expiry date. This leads to a common question: does water have no expiry date? The answer lies not with the water, but with its container and storage conditions.

Quick Summary

Pure water does not go bad, but the plastic bottles or other containers can degrade over time, affecting taste and safety. Factors like heat and sunlight accelerate this process.

Key Points

Water Doesn't Expire: Pure H₂O is chemically stable and does not spoil like food, so in its purest form, it does not expire.
Packaging is the Problem: The expiration date on bottled water refers to the plastic bottle, which can degrade over time and contaminate the water.
Plastic Leaching is a Risk: Exposure to heat and sunlight can cause chemicals and microplastics to leach from the plastic bottle into the water, affecting taste and safety.
Storage is Key for Longevity: Storing water in a cool, dark place away from heat and chemicals is crucial for preventing degradation and contamination.
Properly Stored Tap Water Lasts: Sealed, chlorinated tap water can be stored for up to six months before needing to be replaced for optimal freshness.
Watch for Warning Signs: Discard any water with an unusual smell, taste, or discoloration, regardless of its age, as this indicates potential contamination.

The Science Behind Water's "Expiry"

Water, in its purest form (H₂O), is a remarkably stable chemical compound. Unlike perishable foods that spoil due to bacterial growth, pure water contains no sugars or proteins for microorganisms to feed on. This means that from a strictly chemical standpoint, water does not "expire." So why do we find expiry dates on bottled water, and why does tap water go stale? The key factors are contamination and storage.

Contaminants are the primary reason water can become unsafe or unpleasant to drink over time. Whether it's airborne bacteria entering an open container or chemicals leaching from the packaging, the water's purity is what's truly at risk. When water sits stagnant, it loses its freshness. This change in quality, not chemical spoilage, is what marks the end of its useful life.

The Truth About Bottled Water Expiration Dates

For decades, bottled water companies have included "best by" dates, leading to widespread consumer confusion. The motivation behind these dates is rarely about the water itself. In fact, the U.S. Food and Drug Administration (FDA) has stated that commercially bottled water has an indefinite shelf life if properly sealed. The best-by date is primarily a quality standard set by the manufacturer to ensure optimal taste and is often influenced by factors unrelated to safety, such as old regulations.

The real issue with older bottled water is the packaging. Most single-use bottles are made from plastic (Polyethylene Terephthalate, or PET) which is slightly porous. Over time, and especially when exposed to heat and sunlight, the plastic can begin to break down and leach chemicals and microplastics into the water. This can introduce an unpleasant, plastic-like taste and potentially pose long-term health risks. New research has also highlighted concerns about microplastic ingestion, linking it to various health issues.

Storage: The Critical Factor for Water Quality

How and where water is stored is the single most important factor in determining its shelf life. Proper storage protects against chemical leaching, bacterial growth, and external contamination.

Best Practices for Water Storage

Choose the right container: For long-term storage, opt for food-grade glass or stainless steel. These are non-porous and won't leach chemicals, offering better quality retention than plastic over time.
Avoid heat and sunlight: Store water in a cool, dark place, such as a pantry or a basement. Heat and UV light are major catalysts for plastic degradation and chemical leaching. A garage is generally a poor choice for long-term storage due to temperature fluctuations.
Keep away from chemicals: Water can absorb odors and fumes through porous plastic. Ensure water containers are stored far from solvents, gasoline, cleaning agents, and other strong-smelling substances.
Sanitize containers: Before storing your own tap water, thoroughly clean and sanitize the food-grade containers to prevent bacterial contamination.

How Tap Water Shelf Life Differs

Tap water from a public supply often contains a trace of chlorine, which acts as a disinfectant. This chlorine helps to keep the water safe from bacterial growth for a period of time. When sealed in a clean container and stored properly, tap water can be safe to drink for up to six months. However, the chlorine dissipates over time, and the water may develop a stale taste as it absorbs carbon dioxide from the air.

Unsealed tap water, such as a glass left on a counter, has a much shorter shelf life. It can attract airborne dust, debris, and bacteria. While often safe for up to 24 hours, its quality and taste degrade quickly. Filtered tap water, which has had the chlorine removed, is even more susceptible to bacterial growth and should be consumed sooner.

Signs That Your Water May Be Unsafe

If you have concerns about the safety of your stored water, rely on your senses. Your eyes, nose, and mouth can detect many signs of contamination. Be cautious and err on the side of safety if you notice any of these indicators:

Cloudiness or Discoloration: Water should be clear. If it appears cloudy, brown, yellow, or has a green tint, it could signal bacterial growth, algae, or rust.
Unusual Smell: A strange odor, such as a musty, moldy, or chemical smell, is a clear warning sign that something is wrong.
Strange Taste: If the water has a metallic, chemical, or otherwise disagreeable taste, it's best to discard it.
Compromised Container: Inspect the bottle or jug for any signs of damage, such as cracks, bulging, or a broken seal, which could allow contaminants to enter.

Comparison Table: Bottled vs. Stored Tap Water


Aspect	Bottled Water (Sealed, Plastic)	Stored Tap Water (Sealed, Food-Grade)
Expiration Reason	Quality assurance; degradation of plastic bottle	Chlorine dissipation; potential bacterial growth
Typical Shelf Life	Up to 2 years for optimal quality	Up to 6 months for best taste and safety
Primary Risk	Chemical leaching from plastic (especially with heat/sunlight)	Bacterial contamination if not properly sanitized or sealed
Best Storage	Cool, dark pantry; away from chemicals	Cool, dark pantry; rotated annually

Conclusion: The Bottom Line on Water's Shelf Life

So, does water have no expiry date? Technically, pure water does not expire, but the truth is far more nuanced. The safety and quality of your water are entirely dependent on its container and storage conditions. For bottled water, the expiration date is a quality marker for the packaging, not a safety warning for the water. With both bottled and tap water, the risks of chemical leaching from plastic or bacterial contamination increase over time, especially with improper storage. For maximum safety and freshness, store all water in clean, food-grade containers in a cool, dark place. For detailed emergency preparedness guidelines, resources like the CDC provide excellent information on safe water storage.

Final Recommendation: Don't be fooled by the myth of immortal water. Always be mindful of your water's container and storage environment. When in doubt, refresh your supply to ensure you are drinking the safest, freshest water possible.

Frequently Asked Questions

It is unlikely you will get immediately sick, as the water itself does not spoil. However, over a long time, especially if stored improperly, the plastic bottle can leach chemicals into the water, potentially affecting its safety and taste.

The expiration or 'best by' date on a water bottle is typically a quality guideline for the bottle, not the water. It indicates the period during which the water is expected to taste its best before the plastic packaging potentially begins to degrade.

Properly sealed and stored tap water can last for up to six months, though its taste may become stale as chlorine dissipates over time. For best taste and safety, rotate your stored water every six months.

You can detect if water is unsafe by checking its smell, taste, and appearance. If it has a strange odor, tastes odd, or appears cloudy or discolored, it is best to throw it out.

While it is possible to refill single-use plastic bottles, it is not recommended for long-term use. The plastic is porous, which can allow bacteria to build up over time. It's safer to use a reusable bottle made of glass or stainless steel.

Store water in food-grade, airtight containers in a cool, dark location away from direct sunlight, heat, and chemicals. Aim to store at least one gallon per person per day for sanitary and drinking needs, and rotate the stock annually.

Water left in an open glass overnight is unlikely to be harmful, but it can absorb dust and airborne microorganisms. It may also develop a slightly stale taste as it absorbs carbon dioxide from the air. For optimal freshness, it is better to drink freshly poured water.