What is reverse osmosis and why is water purification important for human health?

Reverse osmosis is the process of removing water from contaminants instead of the usual method of removing contaminants from water. It is a very effective filtration method, but it is not exactly a fast method unless very large, very expensive equipment is utilized (compared to other methods). RO (reverse osmosis) should not be relied on to treat water of microbial safety (read bacteria and viruses) other methods such as chlorination or ultraviolet sterilization should be employed to kill off any living microorganisims since some may be too small to be effictively trapped by the RO process. To the best of my knowledge RO water filtration was originally used by the US Navy as a method of desalination of water on aircraft carriers. For more indepth information try searching wikipedia.