The amount you need to wash your hair and clean your scalp really depends on the individual. Some people can go days and even a week without washing their hair and others have to wash every day. I think you have to pay attention to what your hair needs. If you notice that you are getting build up and your hair feels limp and dirty then wash it. For me personally I cannot wash my hair with water only because although the water may be a natural moisturizer it does nothing to clean my hair. I also cannot co wash for weeks at a time without using shampoo, I have to use a shampoo at least once per week which is sulphate free to clean my scalp and hair and get off the product build up if any. You donít want your pores to clog by not washing thoroughly enough when you need to.
There are a lot of oils that help treat dandruff and dry scalp I know coconut oil is one on them. If you do use oil on your hair you will need to use a shampoo when you are ready to wash it out.