What do you think is there such thing as “bad” water or stale water is something completely different?
Have you ever noticed that stale water has a strange taste?
Ordinary water can easily be infected with microbes, because it contains no sugars and proteins.
More specifically, water that was exposed to the air for a while is soaking up a little carbon dioxide, and part of it is converted into carbonic acid. This means that water changes its chemical composition.
Once carbon acid releases one to two protons i.e. turns into a bicarbonate or carbonate, it changes the pH value because of which its taste is different.
In addition, stale water has been exposed to a certain amount of dust and bacteria.
This does not mean the water is not drinkable, but you should probably think twice before you drink stale water next time.