Does Bottled Water Go Bad?

Dasani bottled water — Plastic bottles of Dasani purified bottled water are given away at a Fourth of July holiday event in Santa Fe, New Mexico. Why do some bottled waters have an expiration date listed? Robert Alexander/Getty Images

The "Big Four" brands of bottled water (Dasani, Aquafina, Glacéau Smart Water and Nestlé Pure Life) each account for $1 billion in annual sales in the U.S. alone. That's a lot of bottled water! Although people drink most of it pretty quickly, some might stock up on it long-term for emergencies or if they get a great deal on bottled water.

But is storing bottled water for a few months (or years) a bad idea? You may have seen a "sell-by" or "best-by" date on your bottle of water, but what does that mean? Can a natural liquid like water really expire?

Why Bottled Water "Expires"

The water isn't actually the issue when it comes to expiration because H₂O doesn't have any sugar, proteins or additives which typically cause food to spoil. The packaging is the real culprit.

The vast majority of bottled water (more than 97 percent) is packaged in plastic. These plastic bottles are ever-so-slightly porous, which "may allow ambient air gases (such as vapors from household solvents, petroleum-based fuels, and other chemicals) to affect the taste and odor of your beverage," according to the International Bottled Water Association (IBWA). It is worth noting that some bottled water manufacturers use a premium level of plastic, which allows their product to hold up better over time but also costs a bit more.

Here's an example of an expiration date on a bottle of water.
Alan Levine/CC By 2.0/Flckr

Interestingly, the U.S. Food and Drug Administration (FDA) doesn't require bottled water manufacturers to list an expiration date because the agency says that the product has an unlimited shelf life. In fact, the FDA doesn't require "best by" or "use by" dates on any products beside infant formula. These dates are usually set by the manufacturers and may not necessarily reflect a decline in quality once the date is reached. "Some companies still place date-based lot codes on bottled water containers, which distribution and retail points typically use to assist in managing stock rotation," says the International Bottled Water Association website. If you see a date on a water bottle, it's generally a two-year expiration period and will say "best by," which doesn't mean you'll automatically get sick if the date has passed.

But there are still some things to consider when drinking "old" bottled water.

Storage Is Key to Preserving Bottled Water

Although the water may be fine to consume past its "best by" date, a lot depends on how it has been stored. Some studies have shown that antimony, a chemical in many plastic bottles, can get into water if it's stored at high temperatures over a number of weeks; however, the increased levels of antimony are not likely to harm someone who drank that water.

The IBWA website says that bottled water should ideally be stored at least at room temperature, ideally cooler if possible, and kept away from direct sunlight and household chemicals. Both excessive heat and sunlight can cause mold or algae to develop in the water, the website notes, turning it into a pretty yucky drinking experience.

So, it's probably not the best idea to leave a case of water in your car over the summer. Although bottled water can withstand some heat-related elements (and almost certainly did already during the shipping and warehouse process), it'll last longer and taste better if stored properly from the point of purchase.