Home Water Treatment Using Activated Carbon: Discussion and guidelines from a 1997 article from the Michigan State University Extension.
HowStuffWorks: Charcoal Filters: What is activated charcoal and why is it used in filters?
HowStuffWorks: Reverse Osmosis: How does reverse osmosis work to purify or filter the water?
Treatment Systems for Household Water Supplies - Activated Carbon Filtration: 1992 article from the North Dakota State University Extension Service explaining in detail what activated charcoal systems can and cannot do.