It seems like cleric in PF can use unlimited times of 0-level spell a day.
By a simple calculation, a level 1 cleric working for 8 hours a day can create 9600 gallons of water a day, by using the Create Water spell.
Am I misunderstanding the rules or is that how the Pathfinder rules work?
If a cleric can provide water for a whole town of people in a desert, this will surely bring a huge effect on desert civilizations. I am not very familiar with the worlds and settings of Pathfinder, did the designers consider these types of things when making the setting?
Best Answer
In short, yes.
Your numbers are correct. A level 1 cleric can cast 4800 cantrips in 8 hours, which would make 9600 gallons of water, just like you say. It's definitely true that a civic-minded cleric could totally solve the water problem for a mid-sized city. If you've got a backup cleric or two, or are willing to take a risk on occasionally not having water for a time, this is a totally reasonable way of generating water.
Your secondary question about how this would effect a desert civilization: You're probably right that the existence of this kind of magic should have a huge effect on how desert civilizations survive and thrive, but generally D&D and Pathfinder setting books don't actually go into the realistic implications of magic. The economics on D&D and PF make absolutely no sense at all, and this is just another branch of that nonsensical tree.