Yes, water does expire. Exposure to high temperatures or to light can make this happen faster.
Every time you heat water (to drink hot tea for example), it starts to lose oxygen and carbon dioxide through boiling; these are gases that destroy the taste of your beverage. This is why many people choose not to boil their water before drinking it, but prefer ultra-pure bottled or filtered water instead.”
But if you simply cool boiled water (to drink ice tea for example), then no oxygen or carbon dioxide will escape because both gases are really unstable at low temperatures; this means your iced tea will last much longer than hot tea. So it’s true that boiling does have a negative impact on the taste.