What happened to this pot
Best guess without knowing your water supply composition; it's not the pan contaminating the water, it's the water contaminating the pan.
Iif you live in an area with certified potable water, it's really mainly visual, it won't hurt.
After comments
Yup, London water - safe, potable… but ugly.
You can either

scrub after every use, or
ignore until it annoys you enough to do a full descale
Buy a Brita jug &amp; never boil unfiltered water.

It is completely harmless, just unsightly.