Activated carbon filtration is not effective on the removal of nitrates or micro-biological contaminates. It does improve appearance and taste of water. It also removes radon and can reduce levels of organic chemicals and lead.
The filter requires frequent changing, depending on the flow rate of water through it. The activated carbon filter can actually harbor microorganisms. This system is normally used in conjunction with chlorine or iodination, which impact the taste and odor of water at the point of consumption.