Aqua Pure easy drinking water systems are one of the most popular home and water cooler filter systems on the market. One of the key benefits of the 3M AquaPure AP under sink drinking water filtration system is its compact design and that it does not require a water holding tank. The Aqua Pure Easy replacement water filter cartridges are easy and quick to change and are designed to fit the standard B2 head. Furthermore, the AP Easy Drinking Water Systems and AP Easy Cooler Series have a 1/4" OD Quick Connect Fittings on the inlet and outlet. Filter heads with a B4 designation (small print on head) have a special key, we do not offer filters for the B4 head. Not compatible with Whirlpool UltraEase models WHCF-SUFC, and WHCF-SUF.