For all wondering why the Mayflower needed beer and why he was disgusted by drinking water is that back then water would make one incredibly ill due to pasteurization not being invented yet, however in the process of making beer you boil and thus kill the bacteria making it the only safe thing to drink as water was filled with these bacteria. It would be a long time before someone realized how to make water safe to drink.
Is there any sort of historical source for this claim? The British navy provided grog to its sailors, but I've never heard this regarding the Mayflower. I am, however, very familiar with the popular historical fallacy that says the ancient Romans drank watered wine because their water was unsafe. Which is untrue.
Also, if boiling in the process of brewing beer is what made the beer safe to drink, why would they not just boil water before drinking it and not bother with the beer, which was more expensive and time consuming to produce?