I've been looking for information on dry scalp because it can cause itching, flaking and shedding. I found this article on it: Can Dehydration Cause Hair Loss? and this Drink Water for Stronger Hair
So it seems that not drinking enough water can lead to dry skin and implicitly to dry scalp which can lead to unpleasant things like shedding, itching and flaking. That's really good info to know. The normal amount of water to drink per day is 8 cups, of 8oz each, that's about 64 oz or 1.9 liters. This is something to consider if you're struggling with dry scalp.
Oils can be used locally, either in small amounts as a leave-in or in heavily as a pre-wash treatment. More info on that and other scalp issues/treatments here: Flaky (and/or itchy) scalp causes and treatments