PETSTANDARD Replacement Filter Compatible with Whisker City® Water Fountain. These are PET STANDARD branded filters and are not created or sold by Whisker City®. Pack of 10 Filters Filter Measurments: 5.0" x 2.5" x 0.25" Double Filtration System: Composed of a cotton layer and activated carbon. Effectively to filter hair, heavy metals, keeps water fresh and improve the taste of the water. To prevent the activated carbon dust from shedding into water, please soak the cat fountain filter in water for 2 minutes then rinse thoroughly under running water before using. Change every 1 to 2 weeks in summer and 2 to 4 weeks in winter. If multiple pets are using the fountain, more frequent replacement will be necessary. Please feel free to contact us if you have any questions about our products, we'd like to help you!