I realise of course that the beer from back then wasn't nearly as strong as today's beer. And infant mortality in general was higher due to many other reasons. But would the back then normal and average alcohol consumption still have made a difference? Were people even aware of a connection between alcohol and problems with pregnancy /infants?
More can always be said, but this question in that formulation "they didn't drink water so they drank beer, what about FAS?" has popped up several times. This thread has answers by u/SpicyBaconator and u/Noble_Devil_Boruta, while u/rocketsocks puts in their oar in this thread.
These answers found by a reddit search, keyword 'fetal'.
Your first sentence is not exactly true. Generally most people did drink water.
This excellent post from /u/sunagainstgold and linked to in the FAQ discusses water drinking.