The Pure filter is designed for customers with city water because its focus is removing fluoride and heavy metals.The Nano filter is designed for customers with well water because its focus is removing bacteria, viruses, and cysts. We also recommend the Nano filter for customers with hard water as it's better at removing sediment, so it will keep your filter lasting longer!Both these filters are interchangeable with your pitcher or jug, so you can always swap them out if your needs change.And to see a full list of everything these mighty filters remove, check out our Testing & Certifications page. We're always updating that and testing for new contaminants, so feel free to check back on it if you don't see a contaminant listed there!