Why does my bottled water have an expiration date?
Does this stuff actually go bad?
Hi everyone, Julian here for DNews.
Have you ever left a glass of water out overnight, and the next day taken a drink and noticed
it tasted funny?
Does that mean the water is going bad, what’s happening here?
Well the water itself doesn’t have any sugars or proteins like food so microbes aren’t
consuming it and rotting it.
However, that’s not to say the chemistry of the water hasn’t changed.
By being exposed to air, the water absorbs some CO2 and a tiny portion of that, about
0.13%, is converted into carbonic acid.
Some carbonic acid will then lose a proton or two, forming bicarbonate and carbonate
respectively.
This lowers the pH of water, making it slightly acidic, and changing the taste.
So does that mean it’s unsafe?
Probably not, no.
Unless you were a shellfish.
Carbonic acid forms about 4 million times more bicarbonate than carbonate, and shellfish
need carbonate to build their shells.
The bias towards bicarbonate production means they have less to build their shells from.
Not only that, but the higher acidity can actually dissolve shells.
Since the industrial revolution, the ocean surface has become slightly more acidic.
So if you love oysters, there’s another reason to care about CO2 in the atmosphere.
Anyway if you’re a human, the small shift in pH isn’t going to be what hurts you.
The problem is water in an unsealed container has been exposed to bacteria.
Most tap and bottled water has chlorine additives, which will keep the microbes from multiplying
for a day or two.
But after that they can go crazy.
Water left outside can also start to grow algae and host mosquito larvae, which will
make you sick and is gross to think about, but not as gross as thinking about the dust
inside your house landing in your water!
It can be purified with chemicals, like iodine or chlorine, or it can be filtered and boiled
and it’ll be good as new.
Again, it’s not the H2O breaking down and going bad, it’s just hosting other nastiness
that spoils the taste.
Our ancestors didn’t have the benefit of germ theory or chemical purification, so when
their water became unsanitary, they had to come up with a different solution.
When they set out for long voyages, europeans sailors had stores of water in wooden barrels.
After a few weeks though, it would start to grow algae, so to get around this, sailors
also brought along beer.
And when the beer ran out, they switched to that old pirate favorite, rum.
The alcohol in the beer and rum killed off bacteria, but the side effect was drunken
sailors early in the morning.
In fact, British sailors actually got a daily rum ration until 1970.
Now though we can store water indefinitely without having to worry about its safety,
provided it’s stored correctly.
The CDC says commercially bottled water is the safest, but it should still be stored
out of direct sunlight.
Some plastics release a hormone disruptor called bisphenol-A, or BPA, into the water
when heated.
Plastic bottles are also permeable so water should be stored away from pesticides and
gasoline.
Aside from that though, you don’t have to worry about the expiration date on bottled
water.
That’s a holdover from an old New Jersey law that has since been repealed because there’s
no scientific evidence to support it.
Gotta love it when science informs lawmaking.
So now the question is, how much water do you actually need to drink?
Trace covers that here.
Have you gotten sick from drinking water?
Did you switch to rum?
Or do you have any other questions you want us to field?
Let us know in the comments or on facebook or twitter, subscribe for more, and I’ll
see you next time on DNews.