I am not sure what our city puts in water, but testing right from the cap I do get ammonia levels. So it isnt the splitting that is causing the ammonia to show.
We may be getting ourselves confused here. You mentioned not wanting a conditioner that creates ammonia, which I assume is the chloramine issue that I understand breaks apart chlorine/ammonia. Colin has explained this.
The ammonia in the tap water could be ammonia. It is possible for tap water to contain ammonia, or nitrite, or nitrate. A conditioner that detoxifies ammonia would convert the ammonia into ammonium, and by the time this becomes ineffective the plants and bacteria would have taken up the ammonium so the problem is solved.
Am I missing something?