How many days before your hair gets greasy/needs washing?

Lock'd, I can tell you that washing with just water does clean the hair sufficiently. My hair always feels really clean once it's dried after I've just washed it with water. The only difference I notice between using shampoo is your hair smells nicer and I found my hair got greasier a day or two sooner than to wash with water. I still wash my dreads with just water, mostly cus my shower is shit and won't wash shampoo out properly.