i never use anything but water to wash my body(and my body isnt disgusting covered in dirt) and have done the 6 week challenge... i lasted about 14 months with out washing my hair. and now i wash my hair once a fortnight ish
You can use apple cider vinegar and bicarb with a hot rinse.
I think most hairdressers would tell you you have to wash your hair.. its their business and they want you to buy products!