http://www.newscientist.com/article.ns?id=dn8187
If only we could see in those tanks! Fronds of weed sloshing backwards and forwards as the tank moves.....empty cigarette packs floating with beer cans on the surface, slime growing on the inside surfaces of the tank.......(bit imaginative). But you still don't want to drink directly from it. If only the beverage containers could be filled with bottled water! Always worth taking a small bottle of Volvic of your own just in case.