Dirty water from groups of slayer espresso machine

Hello everyone !

I work as a barista in Queensland, Australia. And recently in the early morning I found the water is yellow when I tried to flush out the stale water in boiler tank. It was shocking. Because we cleaned our groups with chemical everyday. And it’s brand new slayer espresso machine and we are not super busy cafe. So I’m not sure how it would happen? And it would be awesome if anyone have idea how to fix it please ! Thanks for the help !

First row from left is water from filter, and second to fourth glass are water from different groups; second and third row are repa