Another consideration is that cisterns were used to collect rain water to provide pure water for castles and towns. If you weren't drinking it, you really didn't need a cistern in most of Europe. From my manual labor days, I can suggest that another reason people drank beer and wine is for the analgesic effects. Alcohol helps the body to relax and helps kill the pain of aching muscles, serious considerations when you don't have Aleve in the medicine cabinet. As for feasts, they were often about revelry and conspicuous consumption.
Good vintages are more worthy of note than water.
I have observed the discussion about whether people in the middle ages drank water, but I haven't followed it very closely, as the absurdity of suggesting otherwise is obvious to anyone who has actually read much in the documents of the time. This is based on Friar Felix's own lengthy account of his travels. Wine, particularly in Palestine which was under Saracen control at that time, was carried separately, usually well-hidden in the bottom of bags or boxes, to avoid the disapproval of the Muslims, who were likely to pour it on the ground if they saw it. Friar Felix frequently comments on the flavour of various streams and wells they stopped at on their way. Some of them he spoke of highly.