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

Fact 2: Boiling is the safest method of treating water.

Given the two facts above, answer the question "What can be done to water to remove harmful substances before drinking?" with the following options: 
- evaporation
 - vaporization
 - Dipping a magnet into it
 - hydration
 - Mixing in heavy metals
 - Cooking
 - Boiling it
 - Adding purified water to it


 

       Boiling it  