yeah, such a silly myth. People have known you can make water safe by boiling since forever. This myth also often dispelled along "they drank it for safety and didn't get very drunk because it was very week beer" like they couldn't just drink more of it until they got as drunk as they wanted.
It's actually really difficult to get drunk off of weak beer (about 2%), you quickly reach a pain point when it hurts to drink more liquid. And I suspect the dilution also slows uptake.
