Dry itchy scalp - UK, Hardwater!

The area I live in has hard water. Even though I've been using the hello klean shower head filter it hasn't made much difference.

My hair looks oily and dark even after washing, my scalp is dry and itchy. I have noticed flaking and now am considering buying a clarifying/detoxing shampoo, any recommendations? I might try the L'Oréal detox but is there other ways to get rid of the itchy and dry scalp?