Quote Originally Posted by Lukas Werth View Post
circular patches on the negative with a peculiar pattern inside, formed by respective areas of lesser density
My guess of the most likely cause is a dimpled bottom on the developing tray.

You say you use gloves and press the negatives into the tray, and this could certainly be the cause but the pattern doesn't look like a set of fingers. If your gloves are powdered latex then some of the powder may be getting on the negative.

Distilled water is not the culprit.