49er,
Unless you plan on polishing, don't wash your car with dish soap. Zaino products are protectants , not polishes (I think) so you didn't really do anything to remove the water marks.
In general, to remove water marks most people have had very good results with vinegar (white distilled). Just pour some in your bucket with water (I'm not exactly sure about the mixture, 50/50 maybe?) and use that to wash the car. This *should* get most of the water spots off, and if not you will just have to try to polish them out with an abrasive polish.
After all of that's done, THEN you can apply your Zaino.
As a rule of thumb, unless you plan on doing a full polish don't use dish soap. Get a good car shampoo instead, especially after you detail.