Why does my coffee taste of chlorine?

Because there is chlorine in it, and coffee is unusually good at revealing it.

Why coffee shows it up

Chlorine and chloramine are added to municipal water at concentrations most people never taste in a glass. Brewing concentrates them, and the compounds interact with coffee’s aromatics — flattening them and adding a distinct pool-like or medicinal note.

The effect is stronger in light roasts, where there is more delicate aroma to lose.

Removing it

Any activated carbon filter. A jug filter, an in-tank cartridge, a plumbed-in filter — all of them adsorb chlorine effectively. This is the one thing every filter does well.

Standing water for a few hours removes free chlorine as it off-gasses. It does not remove chloramine, which many utilities now use instead precisely because it is more stable.

Boiling helps with chlorine, not with chloramine.

So if standing or boiling does not fix it, your supply is chloraminated and you need carbon.

Timing

Chlorine levels vary through the year and after mains work in your area. A sudden change in how your coffee tastes, with nothing else altered, is often this.

Also check the kettle

A kettle with old scale and residue contributes its own flavours. Descale it — people filter the water and then boil it in something unpleasant.