Knowing the importance of water, and of course – thirst, many people leave a glass of water on their nightstand before going to bed in case they wake up during the night feeling thirsty. And all of you who have done this, or do it regularly, will know the strange taste that the water has in the morning.

When water is left in an open glass it becomes more tractable to any dust particles and bacteria that are air-borne. There are also subtle chemical changes that happen overnight which actually change the composition of the water, making it so slightly acidic.

Once water is left exposed to air, it begins to absorb carbon dioxide, a small part of which is transformed to carbonic acid. This means that once the water is exposed to air, it is more likely to change its chemical structure. Carbon acid transforms into carbonate or bicarbonate once it releases one or two protons, causing it to change the water pH. This process makes the water change its taste.

Is it unsafe? Probably not – well, unless you are a shellfish. Carbonic acid forms four million times more bicarbonate than carbonate, and shellfish use carbonate to build their shells, so they would have less carbonate to work with.

The levels of acidity in the world’s oceans have risen since the industrial revolution, due to the extra carbon in the air.

This slight acidity change in the water cannot hurt you however, but water that is exposed to air for a longer period, will be exposed to bacteria, which can later lead to the growth of algae and possibly mosquito larvae.

On the other hand, bottled water should be safe indefinitely as long as it is stored correctly.

So, next time you leave your glass on your nightstand, think about it before you go for it in the morning.

Don’t forget to share, cheers!

See also: See What Happens When You Drink Water On An Empty Stomach