> New York City’s water (including drinking water) is unfiltered, making it the largest unfiltered water system in the country. Were New York to begin filtering its water, it would cost the city approximately 1 million dollars per day to operate the filtration plant.
They have hundreds of sampling stations to check daily.
https://www.nytimes.com/2025/05/01/nyregion/nyc-tap-water-qu...
This causes some issues for observant Jews, because the water technically might not be kosher.
https://oukosher.org/blog/consumer-news/nyc-water/
https://www.nytimes.com/2004/11/07/nyregion/the-waters-fine-...
Filtration isn't common.