Why Does Bottled Water Have an Expiration Date?

Why bottled water has an expiration date

“Expiration” on water is typically a label convention rather than a true spoilage deadline. Manufacturers use dates for a few practical reasons:

• Quality assurance: setting a time window in which taste and odor remain consistent.
• Packaging performance: plastic caps, liners, and bottles can slowly change with heat, sunlight, or long storage.
• Inventory management: retailers rotate stock more reliably when a “use by” date is visible.
• Traceability: date/lot codes help locate and isolate a production run if there’s an issue.

A common industry practice is to print a date around 18–24 months after bottling for still water in plastic, even though the limiting factor is usually sensory quality rather than microbiological spoilage.

What actually changes over time in unopened bottled water

Taste and odor drift is the most common “expiry” driver

Water can pick up faint “plastic,” “fruity,” or “stale” notes over time, especially if bottles are stored warm or in direct sun. These changes are usually tied to very small amounts of packaging-related compounds and to oxygen exchange through caps/liners.

Carbonated water is more time-sensitive

Sparkling water can lose carbonation as CO₂ slowly permeates through packaging and seals. If your bottle is carbonated, the “best by” date is far more likely to reflect a noticeable quality drop (less fizz) rather than safety.

Heat and sunlight accelerate everything

A bottle stored in a hot garage, car trunk, or near a sunny window will age faster than the same bottle stored cool and dark. “A couple of summers in the heat” can matter more than the calendar date.

Packaging migration: what it is and when it matters

Most still bottled water is packaged in PET plastic. PET is widely used and generally stable, but like many food-contact materials it can release trace substances under certain conditions (notably heat and long storage).

One example often discussed is antimony, a catalyst residue that can be present in PET at trace levels. Drinking-water standards for antimony in the U.S. are commonly referenced at 0.006 mg/L (6 µg/L). Research shows antimony migration tends to increase as storage temperature rises, with higher temperatures (for example, around 50°C/122°F) producing larger increases than typical room-temperature storage.

The practical takeaway is straightforward: normal indoor storage is rarely the worst case. Heat exposure is the variable that turns “months or years” into “weeks or months” for quality changes.

Microplastics and “bottle aging”: what recent data suggests

Beyond taste, many people worry about microplastics and even smaller nanoplastics. Recent laboratory work using advanced imaging methods has reported that bottled water can contain plastic particles on the order of ~240,000 particles per liter on average, with a large share in the nanoplastic range. Not all particles necessarily come from the bottle alone; caps and filtration components can also contribute.

Two points are important for practical decision-making:

• Science can measure these particles far better than it could a few years ago, so higher counts may partly reflect better detection—not necessarily a sudden change in manufacturing.
• Health impacts are still being studied, but minimizing heat, sunlight, and physical abrasion (for example, bottles rattling in a hot car) is a reasonable, low-cost precaution.

How to interpret the date on your bottle

Bottled water packaging can show different kinds of dates. Knowing which one you’re looking at helps you use it correctly.

Best-by date

This is a quality target. It indicates when the producer expects the water to taste “as intended,” assuming reasonable storage conditions.

Bottling date or lot code

This supports traceability and inventory rotation. It may look like a stamped code rather than a normal calendar date.

“Sell by” date

This is for retailers, not a safety deadline. It helps stores manage stock and reduce customer complaints about off-taste.

Best storage practices to keep bottled water “fresh”

If you want bottled water to stay neutral-tasting and low-odor for as long as possible, storage conditions matter more than the printed date.

1. Store in a cool, dry place (indoors is usually better than garages or sheds).
2. Keep away from direct sunlight and heat sources (windowsills, radiators, hot cars).
3. Avoid storing next to chemicals with strong odors (paint, gasoline, cleaning agents); plastics can pick up smells.
4. Keep bottles sealed until use; once opened, treat it like any drinking water and consume promptly.
5. For emergency supplies, rotate stock periodically and prefer cooler storage locations.

When you should not drink it

A printed date alone is not the best indicator. Instead, use condition-based checks. Discard bottled water if any of the following apply:

• The seal is broken, the cap is loose, or the bottle has leaked.
• The bottle is visibly damaged (warped, cracked, or unusually brittle).
• There is a strong off-odor, chemical smell, or clearly unpleasant taste.
• It has been stored for extended periods in high heat (for example, repeatedly left in a hot car).

If the bottle is sealed and stored cool and dark, the “expiration date” is usually a quality guideline—not a hard safety cutoff.