There is residual chlorine or today more likely chloroamine in tap water. Part of the reason for that is to keep pathogens from growing in the pipes. Though depending on season and basic water quality there may be none.

If you care, ascorbic acid or one of it's salts line sodium ascorbate reduces[1] chlorine and chloroamine. Takes just a tiny amount, works instantly.

[1] Chlorine -> chloride. chloroamine-> chloride + NH3.