So I've heard before modern sanitation and germ theory people used to drink things with very low alcohol contents because they were safer than the water supplies nearby. How true is that and how did places that didn't drink alcohol (like most Muslim communities) cope?
Ah yes, The Water Thing. It's not as bad as popular imagination believes it is. The Water Thing is in the VFAQ, specifically this section (Middle Ages, then Health & Hygiene, in case your browser doesn't take you directly there).
For other posts on the matter, we can turn to u/idjet, who has an answer that links previous answers of theirs on the topic. u/CptBuck also here addresses how desert civilisations do for water.