We camped at Bruin lake camp ground with the Great Lakes TearJerkers this weekend and spent time in Hell, Mi. There is an area in the entrance to empty tanks and or fill up fresh water. I had just replaced the filter in our CX90 filter which has an outer ceramic shell which is fortunately scrub-able because with in a few seconds of turning on the water the nice white filter turned brown.
Judging by what was in the toilets this is silt.
The point is that while this is probably potable what was left in the tanks and water heater of the 5er that filled up at the same time will be with him a long time