They work like a drip coffeemaker. Water is poured in the top and filters by gravity through the filter to the bottom. These filters are quite slow and handle only small volumes of water. Faucet-mounted AC filters are small units attached on the end of a standard kitchen faucet. They are convenient to use, but because of their size require frequent change.
Some units have bypass valves, to filter just the water needed for cooking and drinking.
They are installed on the cold water line, and some units are installed with a bypass to separate cooking and drinking water from other uses. Under exceptional circumstances all water may need to be treated by AC filtration. A high-volume unit may be installed at the point of entry to the house if all water needs to be treated. In recent years, several independent laboratories have tested AC filtration equipment for effectiveness in contaminant removal. Based on the testing results of these organizations, general recommendations can be made regarding AC filtration.