Abstract: A water diffuser is configured to extend from the discharge outlet of a pet fountain and to receive water from the outlet of the pet fountain's water pump. The the diffuser includes a perforate tubular diffuser section that can be releasably coupled or otherwise anchored to part of the fountain by a connecting or coupling section that may be tubular and imperforate. The diffuser can include an insert disposed within the diffuser that is dispensed or released into water flowing through the diffuser. The diffuser may also include a filter for removing contaminants from water flowing through the water. Where used together with an insert, the filter can be disposed within the diffuser upstream of the water treatment for filtering water flowing through the diffuser before treating the flowing water.