Is it OK to drink bottled water after the expiration date in Japan?

Let’s say you’re at home, going through your disaster preparedness kit, and you find a bottle of spring water you bought a long time ago in case of emergency. Checking by the cap, you see that the expiry date was a few months ago, and decide to use it to water plants or top off the washing machine instead of drinking it. Well, congratulations; you just wasted perfectly good water.

Alright, “perfectly good” might be an overstatement since we’re still not sure what the microplastics floating around in there can do to us, and “waste” is also a little harsh since plants are our friends too. But the point stands that you could have drunk that water and it would have been more or less as good as the day you bought it.

This is because according to the Secretary General of the Japan Mineral Water Association, the “expiration date” on bottled water isn’t used for the same reason that it’s used on perishable food. This is actually the date at which water inside the bottle is expected to have evaporated so much that the bottler cannot guarantee the amount written on the bottle is inside anymore and could be held liable for false labeling.

Water bottles in Japan are usually made of a type of polyethylene terephthalate (PET), which is slightly permeable to water vapor. Some tests have found that when stored at around 25 degrees Celsius around two to three milliliters of water vapor can escape per month. Also, in the hot summer months of around 37 degrees Celsius, that rate goes up to about 4 milliliters per month.

Meanwhile, the Measurement Act of Japan states that the actual contents of a bottle must be no less than two percent under the amount listed on the label for bottles under 500 milliliters and no less than 10 milliliters less than the labeled amount for bottles 500 milliliters and up. So, bottlers of water simply calculate the rate of evaporation and release through the PET bottle, apply it to the legal threshold, and an expiry date is born, but it’s not the water that expires. It’s the label on the bottle that does.

Of course, this is a separate subject from contamination from chemicals inside the plastic of the bottle, and it’s possible both things could be occurring at the same time. But since evaporation happens rather quickly, would there even be enough time for significant amounts of potentially hazardous chemicals to seep into the water from the plastic?

Going by the rate of evaporation found in studies, at two milliliters per month we can expect a 500-milliliter bottle to be empty in 20 years and 10 months. In the case of chemicals from the plastic entering the water, known as “leaching,” the most worrisome elements are antimony and germanium. Under normal storage conditions, it would take about 71 years for enough antimony to enter the water to surpass Japanese safety standards and about 15 years for the germanium levels to surpass those deemed safe.

Mind you these are just the standards, which tend to err on the side of caution, meaning one 15-year-old 500-milliliter bottle of water — wait… 140-milliliter at that point — probably won’t send you straight to the ER. Even factoring in things like the lower concentration of water as it evaporates and the diminished leaching as the surface area shrinks, you’re still looking at about a good nine years or so before standards are exceeded.

One big caveat to all this is that it only applies to Japanese water that has been sterilized to Japanese standards and in bottles made to Japanese standards. Every country has its own standards, including what it considers the allowable limits of antimony and germanium to be, so do your own research before consuming 10-year-old bottles of water anywhere outside of Japan.

Microplastics are also still a bit of a wildcard, in terms of their effect on the human body and how rapidly they break down in a typical Japanese PET bottle of water. Most microplastics are said to enter the water during bottling at the factory, so the bulk of it will already be present in a brand-new bottle anyway, with only a relatively moderate increase over time if stored securely. Unfortunately, there don’t seem to be any studies on microplastic contamination over very long spans of time, such as 10 years.

▼ In other words, if you’re worried about microplastics you really shouldn’t even be drinking new plastic bottles of water.

This information has recently been trending online in Japan and many came out in agreement with it, either using their own theoretical knowledge or personal experiences. Others still felt it wasn’t worth the gamble.

“If the water can escape, can’t things like bacteria get in?”

“Molecules like water and carbon dioxide are 0.3 nanometers, about the same as gaps in permeable plastic, but a virus is about 20 nanometers so it can’t get in.”

“If I leave water out, I just use it for laundry.”

“I’m still just going to use it for cleaning and watering plants.”

“Water is always fine, isn’t it?”

“I had some water that I’d been keeping for seven years in case of emergency. I drank it when I replaced it and it was fine.”

“I’ve been given expired ones before and there definitely seemed like less water inside.”

“If the bottles are breathable I probably shouldn’t store them next to the toilet.”

“If the bottle is shriveled that’s good because the air pressure outside is collapsing it. If the bottle is old and a normal shape, air has gotten inside and there might be bacteria too.”

“I’m still going to pour it down the drain anyway. Why take a chance?”

Whether you’re willing to crack open a seven-year-old bottle of Japanese water is entirely up to you, but the key takeaway from all this is that the expiration date written on it has absolutely nothing to do with its quality, so feel free to hang onto it at least a little bit longer than that.

Sources: Yahoo! Japan News, The Sankei Shimbun, withnews, Ministry of Economy Trade and Industry, Japan Soft Drink Association, Japanese Journal of Food Chemistry and Safety, Food Safety Commission, Hachima Kiko

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