Tap water is treated (UV and chloride disinfecting), but is largely not filtered: https://en.wikipedia.org/wiki/New_York_City_water_supply_sys...
The untreated NYC water has tiny crustaceans in it, which make it not Kosher, which is why thee bagels from a Jewish deli in NYC are so good. Go figure.
https://newsfeed.time.com/2010/08/31/drink-up-nyc-meet-the-t...