Variations of your question are frequently asked on this sub. See, for example, this post answered by u/sunagainstgold, this answer by u/Qweniden, and this thread in which u/butter_milk both addressed the question directly and linked to additional posts asking the same thing. The bottom line is that alcoholic beverages were not commonly used as a safe substitute for water. Medieval people knew what water was safe and what was likely to be contaminated.

As for Daily Life in the Middle Ages, Newman does assert that "Beer was a far more hygienic beverage than water during the Middle Ages because of the lack of technology for purifying drinking water," but gives no evidence that people actually chose to drink beer for this reason. In fact, he goes on a few pages later to contradict this idea in his description of drinking water and the sanitary regulations imposed on it. People drank alcohol in the Middle Ages for the same reason they drink it today - they liked it.