There are people who leave a glass of water beside their bed, just in case they wake up during the night feeling thirsty.
Those who have done this or do it still do, know the strange taste that the water has the next morning.
The water unlike food doesn’t contain proteins or sugars that the microbes thrive on. Therefore we can’t say that the microbes are capable for its strange taste.
However, the water that is left in a glass during the night is more susceptible to air-borne bacteria and dust particles.
Then again, if water is exposed to air, it will absorb carbon dioxide, and a small part of it is converted into carbonic acid. To be precise, this implies that the water which is exposed to is likely to change its chemical structure. To be more specific, carbon acid converts into bicarbonate or carbonate when it releases one or two protons that in turn can change the water pH level. This change also affects the taste of the water.
While this doesn’t have to mean that water that has been on your nightstand all night is harmful to drink, but it is definitely something worth considering because of the fact that it has collected lots of dust and air-borne bacteria. Therefore, the next time you feel thirsty when you wake up, simply hop to your kitchen and pour some fresh water.