When classified based on mechanism and function, filters can be classified as Pitcher, Faucet, Gravity-fed Drip and Reverse Osmosis.
Pitcher filters use granulated activated carbon and they are effective with removing chlorine, hydrogen sulfides. However, these filters are not ideal for other contaminants like fluoride, VOC’s and various metals.
Faucet filters are those used to attach to kitchen faucets. The performance and the range of substances acted upon doesn’t really differ from Pitcher filters.
Gravity fed filters are considered the best form of water filtration due to the ultra-efficient filtration process they employ. They are are capable of filtering a wide range of substances including chlorine and it’s by products, fluoride, metals, and a myriad other harmful elements. Gravity fed filters operate without electricity and they typically consists of two chambers which provide two levels of filtration in the process. This allows for the process to be slow and effective and in case you may need specific examples, the ProOne G 2.0 is one such example on the market today.
Reverse Osmosis Filters are usually used as permanent filters under the sink and they employ a semipermeable membrane for filtration. They also have a wide range of chemicals to filter from the water but are not as effective as Gravity fed filters in that they are not able to remove VOC’s and pesticides which may be present in the water.