Baking Soda (2 tsp aluminium free) and fill bottle with clean Water (preferably chlorine and fluoride free) - that’s it
Optional: add a couple of drops of Essential Oil - Lemon, Orange or your choice.
Hair Conditioner:
Organic Apple Cider Vinegar (approx 3 tbsp) and fill bottle with Water. It removes tangles, and no your hair does not smell of vinegar. Simple, inexpensive, no nasty chemicals.