!Do not use this answer for cheating, please only use my answers to check your own!
Before tap water was found, people would use rocks, gravel, and sometimes even thick cloth to filter water. If you do not filter water, there is a huge chance that bugs, bacteria, viruses, and other things may be entering your body. Today some houses still have the past was of filtering, with rocks and gravel. Except chlorine is used to kill any bacteria that was left over the rocks and gravel may of missed.