Troubleshooting: What is the water filter sponge? Why to use: Capture and filter fine impurities and particles, to improve humidifying efficiency in a healthier way. When to change: Generally lasts 1 month depending on hardness of water. Where to buy: Please search B09ZY9N6PD or LEVOIT 10-Pack Humidifier Replacement Filters on Amazon. Note: Distilled/ purified water is preferred for your health. Specifications: Product Dimensions: ?9.7 x 8.1 x 13.4 in / 24.5 x 20.5 x 34 cm Whisper-Quiet Operation: ? 30dB Effective Range: 215-505 ft² / 20-47 m² Material: BPA free, suitable for babies and adults.