The rivers around here are polluted from industry 50 years ago with those "forever chemicals".   There are many carpet and flooring mills here and all that stuff that makes your carpet stain proof and easy to clean, it's what's in the water.
Higher than the rivers are many springs and they're okay to drink from.  Lots of people get their drinking water from springs and the city water, pulled from the polluted river, is only used for washing and flushing.