High levels of arsenic are present in multiple areas of the city and conurbano, Though not everywhere. As far as I recall it's mostly dangerous for children/long term. Other than that it's usually ok.
There was an article in la nación a while ago which shows all the effected areas, should come up if you search.
Hello, everybody. In CABA we have drinking water. Maybe you would feel more safe by using a water purifier filter or even more simpler, you could boil water.