3 pack filters are compatible with the Dogness App Fountains, Sensor Fountains and Automatic 2.2 litre Fountain only (not compatible with the 3.2 Liter, 2L or 1 Litre Fountains). The freshwater quality promotes hydration for your pet. The 3 stage filter with activated charcoal removes hard water, harsh chemicals, hair and, residue to improve the water quality, and taste. Safe and non-toxic, each filter lasts up to 4 weeks.