You might have noticed that if you ever drink water left by your bedside overnight, it tastes ever so slightly different.

You might put this down to having just woken up, or you might think the strange taste is all in your head.

But as it happens, water does change overnight (and no, it’s not dangerous.)

In a video, Discovery News explains that while you sleep, the water absorbs some carbon dioxide, a tiny fraction of which becomes carbonic acid.

‘Some carbonic acid will then lose a proton or two forming carbonate or bicarbonate respectively,’ the video says.

‘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.’

Crustacean shells are made from carbonate, and the higher acidity can dissolve shells.

The only risk posed to humans by a glass of water is if it is left out for a much longer period of time and is exposed to bacteria as a result.

Source: MetroUK