Sure that the water in the fountain Drinkwell your pet always tastes clean and fresh. Fill Drinkwell Premium Replacement filters that have compartments 6 that evenly distribute the charcoal filter in the long-term deep water. More coal is added to each compartment in order to maximize filtration. Works with Original Drinkwell's, Platinum, fountains and Big Dog (sold separately), but not the Drinkwell 360. Replace the filter every 2 to 4 weeks for optimum freshness. 3 filters in one package. The Drinkwell ® Premium Filters feature six compartments of coal! This evenly distributes the coal for a longer period, filtration of deeper waters. More coal is added to each compartment