Fact 1: Treating water is used to remove harmful substances before drinking.

Fact 2: Arsenic, a naturally occurring substance, contaminates water sources in many countries.

Given the two facts above, answer the question "What is treating water used to remove before drinking?" with the following options: 
- arsenic
 - air
 - cellulose
 - chemicals
 - Collagen
 - loose dirt
 - water vapor
 - ice


 

 arsenic        