The Tommee Tippee Perfect Prep Filter is compatible with the Tommee Tippee Perfect Prep Machine and Perfect Prep Machine Day & Night (each sold separately).Perfect Prep Filter: The Only Filter That's as Effective as Boiling Water Tommee Tippee Perfect Prep Machine Filters remove impurities, contaminantsand bacteria from water to ensures every feed is perfectly prepared and safe for your baby.Specially designed with a unique anti-bacterial filtration system, dispensed water is clean and safe, just like boiled water (without cooling or waiting for the kettle).A light on your Prep Machine lets you know when to change the filter. Prime the filter in cold water for at least 5 minutes before first use to remove air bubbles and particles.For best results, Perfect Prep Machine Filters are recommended to be replaced every 3 months (based on preparation of 6 x 260ml bottles per day).