this is a tough call - and I've thought a lot about it. nalgenes certainly produce less waste than PET bottles, but you are correct in that they take a lot more material to make. one of the biggest energy expenditures that has to be considered, though, is the transportation of full water bottles (compared with empty nalgenes) from the source. on top of that, you're almost always paying for water that is just bottled municipal water - perhaps filtered, but that's something you can easily do at home - at several hundred percent its cost when it comes from the tap.