Usually for well-purified water this should not be. Possible reasons for the phenomenon: a) the water is not clean enough, a change in taste due to the vital activity of bacteria b) the air in the room contains some chemicals that are absorbed by water and change its taste c) the glass from which the glass is made, contaminated - for example, salts of some heavy metals d) all of the above is not, but you poured cold water, and it warmed up in the room. In warm water, all the flavors are stronger