From a chemical standpoint, water is stable and doesn’t break down with time. H₂O doesn’t suddenly “go bad.”

So why do bottles carry expiration dates? The answer lies in external factors:

• Packaging degradation — especially plastic.
• Sunlight and heat exposure — which accelerate chemical leaching.
• Microbial contamination — after a seal is broken.

Think of it this way: distilled water in a sterile, airtight glass bottle could remain safe for years. But that’s rarely how water is stored in everyday life.

Bottled Water: Packaging and Plastic Leaching

Why Bottled Water Has a “Best By” Date

The FDA doesn’t require expiration dates on bottled water. Still, most brands add them — usually 2 years from bottling — to account for packaging integrity, not the water itself.

The Role of Plastic

Most bottled water comes in PET (polyethylene terephthalate) bottles. Over time, especially when heated, chemicals migrate into the water:

• Antimony — linked to stomach irritation at high levels.
• Microplastics — particles shed from the container.
• BPA and phthalates — endocrine disruptors (mainly in older or poor-quality plastics).