Unfortunately, I think a lot of it may be as the standardization is simply not present. How much crevacrol you are actually getting in the Oregano oil you purchase and how long that may actually be present once exposed to air is the question. Trying to drop it into water would likely be ineffective as it first would not mix, then it would oxidize, let alone simply react to ambient sunlight, let alone guarantee any degree of concentration for each bird, I should think.
Right now, unfortunately, while I am enamored with the idea of herbal remedies as pests are building resistance to the current products, and the FDA continues to make life hard for anyone who wants to sell eggs to actually treat birds, I consider Oregano interesting to investigate. However, until better proof is done, beyond those trying to sell the product, I simply feel I am using very expensive herbs to baste chickens.
LofMc