Fountain can be customized with the five interchangeable spout rings included with each fountain. Its quiet， submersible pump passes the water through an activated carbon filter to remove impurities before pumping it into the bowl. Flow control on top cap lets you easily adjust the speed of the water flow while unit is operating - no need to shut it off. To fill the unit， simply add more water to the bowl; maximum and minimum fill lines guide you. Great for multiple pet households. Holds 128 oz. One filter included. Filters should be changed every 2-4 weeks. Utilizes the same filtering technology as all Drinkwell fountains and constantly circulates water to inhibit bacteria.