Hussar said:
Imagine a world where every cleric can "Purify Food and Drink" several times a day. Suddenly clean drinking water everywhere would have a HUGE impact on a setting.
Everywhere? Surely only where such a character -- in OD&D, one at least 9th level (as "several" > 2) -- chooses so to devote him/herself to such labor.
In OD&D, each casting provides for 12 people (for a single meal, is the interpretation I have usually encountered, but YMMV). In AD&D, it's a cubic foot per level.
Of course, the reference is to members of the cleric
character class (and even then, 1st-level clerics cast no spells in OD&D). That does not necessarily include the majority of non-adventuring deacons, priests, pastors, rabbis, monks, shamans or whatever.
In the real world, most human beings need only very basic implements to
boil water for drinking, which goes some way toward purification. Until tea became the fashion, I gather that London lived mainly on liquor.
Continual light is a 2nd level m-u spell or 3rd level cleric spell in O/A D&D.
This is one of those cases in which one must ask how special the PCs are.
If a 3rd-level magic-user or
5th-level cleric is as common in Fantasyland as an electrician is in our world, then of course there should be plenty of magical lighting. Magic has tended to be common enough in Elven enclaves, certainly, and ruins reminiscent of the remnants of anciently advanced civilizations that Conan and John Carter encountered are also often lit with glowing jewels.
Otherwise, one might look at how much interest
players show in taking on the role of Con Edison.