A carefully experimental work shows that concentration of the generated bulk nanobubbles becomes negligible if pure water was used, the equipment was cleaned properly, and certain plastic materials were avoided. The results indicate that trace organic contaminants are necessary for nanobubble stabilization. At present there is no technique available that is able to identify where the amphiphilic molecules (contaminants) come from: from gas source, from the solution surface exposure to airborne contaminants or from the solution itself.