The city is not a State. The Fourteenth Amendment says that States shall not abridge the privileges and immunities of citizens.
As the court's opinion points out (and as others have pointed out in this thread), there are plenty of other legal remedies that can be sought against a city government that allegedly poisons its people through its water system, including voting them out of office and bringing tort claims against them.
As the court's opinion points out (and as others have pointed out in this thread), there are plenty of other legal remedies that can be sought against a city government that allegedly poisons its people through its water system, including voting them out of office and bringing tort claims against them.