The right replacement filter for the Fresco EZ smart pet fountain/drinker (2 litres) from Petoneer is the Petoneer Replacement Filter, which was specially developed for the Fresco Smart Fountain models. These replacement filters are available in sets of 3 filters and provide effective 3-stage water filtration (pre-filter, activated carbon filter, ion exchange resin). The filters should be changed approximately every 30 days, with the appliance reminding you to change them via app or LED display.