And in those days not so easy to boil the water.
People at the time still thought cholera, like many other diseases was caused by "bad air." The investigation that occurred to try to find the source of the cholera helped people realize that cholera was caused by germs, and that sanitation practices needed to be improved.
For hundreds, if not thousands of years, people didn't drink water because it could kill you. They instead drank watered-down ale, wine and hard cider with their breakfast, and during the day while working. At supper and into the evening, they drank the full-strength stuff. Even children drank the watered-down stuff instead of water.