Biofilms show up in many unexpected places.  Many homes and commercial establishments use reverse osmosis water treatment systems to purify drinking water and to make it taste better.  Reverse osmosis systems pass water through a series of membranes which remove contaminants and organic materials.  But guess what?  The water, contaminants and organic materials trapped by the membranes provide a friendly environment for biofilm growth, which in turn reduces the amount of water that can be treated by the system.  It is not so easy to detect in this picture, but the membranes shown here are contaminated with biofilm.