Soap near the water sources is bad. All soap including CampSuds, Dr. Bonners, Ivory, etc. Very tiny amounts in the drinking water can cause you to have the "green apple splatters". It is an old Boy Scout trick if you want to get even with somebody, just put a drop or two of soap in their water. It can make somebody very uncomfortable on the trail. Treating the water doesn't take soap out of it and I'm not 100% sure a filter can take it out either.
Now, as far as rinsing off in the stream there is no real problem. Bacteria that might be on your body is easily killed by treating or removed by filtering. You should treat all backcountry water sources. Seems like I saw that on a sign once..............