If you’ve ever left a glass of water on your bedside table overnight, you may have noticed that it tastes a little strange in the morning.
It turns out this effect is not all in your head – subtle chemical changes that happen overnight can actually change the composition of the water, making it ever so slightly acidic.
But don’t worry; the changes are not dangerous unless you happen to be a crab.
The water itself does not have proteins or sugars, so microbes are not breaking it down like they do with food, so water does not ‘go off’ in the same way.
But its chemical composition does change – as it is left open to the air overnight in the glass, it absorbs some carbon dioxide.
A tiny fraction of this is converted into carbonic acid.
This lowers the PH of water making it slightly acidic, which changes the taste. So does that mean it’s unsafe? Probably not – unless you are a shellfish.’
The slight change in acidity in your glass of water won’t hurt you, however, but the water that is exposed to air for prolonged periods of time – days at a time – will be exposed to bacteria if left out.
This can lead to the growth of algae and mosquito larvae too if left for too long.