My historian friend told me it is true, at least in the early middle ages. You drink watered down alcohol, and eat boiled stews (the concept of just boiling water apparently never dawned on them). Depending on the area, the drinks may be wines, ales, beers, or so on - but not water, not if you can avoid it.
Nobles drink wine with spices.
He doesn't know
He says it's possible they drunk juices, but he isn't certain.
The ambiguity of the Qur'anic ban on alcoholic beverages, meant that wine (usually sold by Christian tavern-keepers) remained fairly popular in Islamic lands over the centuries, as revealed in the verses of Persian poet and mathematician Omar KhayyÃ¡m (1040â€“1131):
"Here with a Loaf of Bread beneath the Bough,
A Flask of Wine, a Book of Verseâ€”and Thou
Beside me singing in the Wildernessâ€”
And Wilderness is Paradise enow." 
In Europe during the Middle Ages, beer was consumed by the whole family, thanks to a triple fermentation process â€” the men had the strongest, then women, then children. A document of the times mentions nuns having an allowance of six pints of ale a day. Cider and pomace wine were also widely available, while grape wine was the prerogative of the higher classes. After the collapse of the Roman Empire, wine production in Europe appears to have been sustained chiefly by monasteries.
In many countries, alcoholic beverages are commonly consumed at the major daily meals (lunch and dinner). Most early beers were in fact highly nutritional and served as a means of calorie distribution. Beer can be stored longer than grain or bread without fear of pest infestation or rotting, and drinking beer avoided the tooth-destroying grit that was present in hand-ground or early mill-ground flours.
In places and eras with poor public sanitation, such as Medieval Europe, consumption of alcoholic beverages (particularly weak or "small" beer) was one method of avoiding water-borne diseases such as the cholera. Though strong alcohol kills bacteria, the low concentration in beer or even wine will have only a limited effect. Probably the boiling of water, which is required for the brewing of beer, and the growth of yeast, which would tend to crowd out other micro-organisms, were more important than the alcohol itself. In any case, the ethanol (and possibly other ingredients) of alcoholic beverages allows them to be stored for months or years in simple wood or clay containers without spoiling, which was certainly a major factor in their popularity.
As a point of paradigm, there are no microscopic bugs in the water. Disease is caused by either demons or an imbalance in the humors. Anybody have any idea why medieval people thought that beer didn't imbalance humors or bring on demons? (Alcohol not being known for rendering its consumer immune to infernal influence, as a rule.)
Clearly it always depends on the location of a place, whether there is good and drinkable water available or not. Medieval people after a short time knew which water made them sick and which not: you can see from the many place-names referring to good or bad water.
Springwater needed of course not to be laced with alcohol, and usually was not.
Medieval towns, however, usually had not enough good water in easy reach of their inhabitants. (Remaining aqueducts, when working at all, were usually no longer cleaned, so their water could not be consumed any more.) Here watered down wine, bear or even vinegar was common. But so was the trade of bringing spring water into towns and selling it there.
Concrete practices vary a lot according to place, time and culture, of course. You have to do your own research of local history and customs for your campaign if you strive for some resemblence to actual history.
(Remaining aqueducts, when working at all, were usually no longer cleaned, so their water could not be consumed any more.) Here watered down wine, bear or even vinegar was common.
Thanks to all for the replies.
My campaign is set in Iberia. The Muslims got many of the Roman aqueducts working again. You mention "cleaning" the aqueducts.... I presume you mean cleaning the stones of algae? Interesting image to think of a bunch of peasants or slaves out in the near-desert scrubbing away. (Of course, a nice PeHe spell would do nicely. It's no wonder the Muslims, being more lenient toward magic, were able to keep the technology of the Egyptians, Assyrians, Greeks, and Romans going....)
Regardless, I'm a little confused... If water in aqueducts brought in water from far-off rivers or lakes, wouldn't the water still be as contaminated as the source?
Not only. Also of incrustations, earth, plants, dead animals, etc. Aqueducts for drinking water needed extensive maintenance.
Yes, of course. For that reason aqueducts collected their water at the springs.
Near UzÃ¨s in the departement Gard you can still find a good example of a Roman system collecting water for an aqueduct, which includes the Pont du Gard and ends at the castellum divisorium in Nimes.
Poking around the internet, it also seems that coffee may have been cultivated in Arabia as early as 1000 AD. In the late middle ages, the drink was apparently popular among sufis for its ability to prevent sleep in late-night religious rituals.
Perhaps for the same reason that our society is generally accepting of alcoholic drink, yet willing to rail about the very downfall of civilization itself when the suggestion is made that marijuana be legalized?
One of my coworkers spent several years in Iraq... The general idea that I got from him was that the Muslims there treat alcohol like most Christians treat premarital sex....Your not supposed to do that, BUT....
most of them do...