I have an update.
About 2 days ago I stopped using water and oil exclusively and used shampoo and deep conditioner. Here is why. My hair was becoming too difficult to detangle and I believe it's because of the lack of slip.
Using a water only regimen, my roots were very silky all of my hair had great shine. My scalp was never dry or had the itchies, and the length of my hair stayed moisturized without any products.
But I had the most ridiculous time detangling. Water and oil don't reduce the friction on my strands the same way commercial, slippery conditioners do. I like to quickly finger comb my hair (we're talking 45 seconds-2 minutes of finger detangling and done). But with water-only, I had to carefully peel apart each tangle and knot.
IMO, all those fears about water only drying out your hair are unwarranted. I have VERY naturally dry hair. It requires constant attention. With water only, it never felt like I had to add any products or moisturizers.
But curly hair needs lubrication to comb. So, I gave up.