Instructions: In this task, you are given a paragraph, and your task is to construct a question from the given passage. Construct question in such a way that (i) it is well explained in the paragraph, (ii) the words may/may not be present in the paragraph, (iii) it should start with what/how/describe. Avoid creating a question that (i) is just relevant to one or two sentences, and (ii) not relevant to passage. 
Input: Water comes through a filter. The filter has small pores to catch pollutants. The filter will catch chlorine, heavy metals, and other chemicals. The filter allows water and mineral ions like fluoride to pass through. The water on the other side of the filter is much cleaner. 
Output:
How does a water purifier work?