Many water filters and water filter cartridges come with the designation “point of use” (POU) or “point of entry” (POE). The description the device is given is predicated on the flow rate capacity as measured in gallons per minute. Generally speaking the flow rate is proportional to the size of the cartridge. This is true for typical dirt/sediment cartridges but is even more critical when using carbon block and granulated carbon cartridges.
Typically carbon filters cartridges with dimensions 2.5” x 10” are to be used at the “point of use”. This means this cartridge should service only one dedicated plumbing fixture. If it is desired to employ a carbon water cartridge at the “point of entry” the cartridge should measure at minimum 4.5" x 10” but more preferably 4.5” x 20”. This will insure there is an adequate flow rate.
"POE" means filtering the entire building whereas “POU” filters one plumbing fixture within the building.