The question Is there a lake whose sole source of water is rain and has a hole at the bottom draining it? doesn't have an answer that answers my question. Also, it has a mistake in it. According to the first comment under the body of the question Is Oregon lake extremely pure water? If so, why?, the lake in the video Clear Lake, Oregon and the lake in the video Adventure Oregon - Lost Lake draining into a giant hole aren't the same lake.
According to this revision the Wikipedia article Pingualuit crater which is also the current revision, "The lake also holds some of the purest fresh water in the world, with a salinity level of less than 3 ppm (the salinity level of the Great Lakes is 500 ppm)." I assume that all solutes except air have an extremely low concentration. I also assume that the dissolved air doesn't have a higher concentration at lower depths despite the higher pressure there because there are no compressed air pockets down there to dissolve into the water and is saturated only at the surface.
My question is
Is it true that all the nongaseous solutes have a concentration by volume that's almost as low as that of salt? If not, approximately what is the concentration of the nongaseous solute with the highest concentration and what is that solute? Could the cause of the high purity be that Pingualuit crater is on high ground so the water is constantly soaking into the ground below draining solutes with it and getting replaced by rain water because there are no outlets to Pingualuit crater?
I realize that probably nothing is totally insoluble in water and so the surrounding rock probably dissolves to some extent.