(Forgive me if this seems rushed; I had a response typed out but my browser had an error and deleted it!)
This concerns me, because water-only washing is generally ineffective. Though it is true that many substances on Earth are water-soluble (hence why water is nicknamed the “universal solvent”), oil—like that produced by your scalp—is not water soluble. Therefore, washing hair without a soap to break down those compounds does not effectively clean hair, no matter what.
Many of the examples we have seen of water-only washing look heavy and oily, especially near the roots. Washing with soap is more hygienic. If you would like a fair-trade, vegan (including no animal testing), organic soap with simple ingredients, consider Dr. Bronner’s Magic Soaps. They are highly concentrated, so diluting them with water helps cut down the harshness of the soap and makes it last a very long time. It’s earth-friendly and very much economical; I have been using the same bottle of soap to wash my body and hair since last summer.
If I had to guess, the change in your washing habits may have something to do with the changed state of your scalp. I suggest going back to your old washing schedule for a few weeks to see if the issues corrects itself. If not, check out our “dry scalp” tag for more specific tips.
However, if the problem persists, please consider seeing a licensed dermatologist if it is within your means. We are not licensed hair care or medical professionals on this site, and as such, we are not qualified to give diagnoses or prescribe treatments. A trained professional will be able to take a look at your situation and specifically suggest what will be best for you. While we do try our best, there are limits to our guidance.
Wishing you all the best,