I’m no expert on ancient Mesopotamian/Egyptian theories of disease, but my understanding is that people knew that water with even a bit of alcohol was significa

I’m no expert on ancient Mesopotamian/Egyptian theories of disease, but my understanding is that people knew that water with even a bit of alcohol was significantly less likely to get you sick than river water, and drinking beer was (in part) an intentional countermeasure. Beyond that, in an ancient context you can’t indefinitely store your boiled water and expect it to stay uncontaminated. If you are on a construction site, boiling all of your drinking water every day before use sounds a lot less convenient than just storing beer. Moreover, if laborers were all drinking water they would still need to eat something.