All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
First of all, we would like to confirm what we have previously told you that there are specialized authorities that are acquainted with these matters in Muslim countries and other countries, like the ministries of health. Hence, you may ask them to give you an answer whether or not this substance is used in their countries and whether or not it is added to water. If it is used, has the authorities taken any procedures to prevent the person who drinks this water from being harmed, like adding a specific substance that removes these harms.
In any case, what we can say is that if it is confirmed that this substance is harmful, then it is not permissible to add it to water in a way that people are harmed as the Prophet said: “There should be no harm and no reciprocal harm.” [Ahmad and Abu Daawood]
Allaah Knows best.