* The Roman historian Pliny noted that "waters vary with the land over which they flow and the juices of the plants they wash". Rainwater was widely prized as the "best", but also the quickest to become putrid, and water from mountain streams was valued more highly than water from wells. Water from snow or ice was generally thought to be harmful, and running water was preferable to still.
* Chalybeate springs (still to be found around Britain) provided water with a high iron conten, beneficial for people with anaemia. Sulphurous springs helped skin conditions. Pliny wisely advised against drinking water stored in tanks because it accumulated "slime or disgusting insects". The Chinese preferred to drink boiled water, and held that drips from stalactites increased longevity.
* In this country, it was not until the early 20th century, with the introduction of chlorination as a means of disinfecting piped water, that water became reliably safe. Until then, people drank beer, which was usually made with better quality water than was easily available, or tea, made with boiled water. During the 19th century, beer was served in schools and hospitals. Alcoholism was widespread, and concern about this was a driving force in the movement to provide safe drinking water for everybody.
Source: The Cambridge World History of Food