Reverse Osmosis provides an even higher level of filtration over carbon. RO effectively removes dissolved particles (like acid, salts, nitrates, pesticides, arsenic etc). You really don’t want any of these particles in your water as apart from being unpleasant, the chances are the particles may contain bacteria.
Like with all things, there are downfalls of using Reverse Osmosis filtration, as whilst it removes everything from the water, it also removes beneficial minerals that also improve taste. These beneficial minerals can however be replaced in the water with additives. RO filters work very hard by using a process called cross flow that constantly cleans the filter of debris. This means a fixed drain is needed as a lot of water does not get through the filter and needs to be flushed away.
Reverse Osmosis is ideal when the water source is unknown or is known to carry contaminants in the water.