Hundreds of people were stricken with diarrhea and vomiting attacks after drinking tap water in the Pardis neighbourhood of Tehran.
Residents have been urged to use bottled water for the next 24 hours while the matter is being investigated, according to Javan News.
Reports indicate that a crack in the pipes has led to pollutants entering the city water supply.
Officials did not confirm the number of people affected by the toxins but they indicate that there have been no life-threatening cases so far and hospitals are dealing with the patients.
The crack has been identified and experts have visited the site and examined the repairs, says a health ministry report.