Wells are cheap, yet important buildings in order to put out fires in close proximity and prevent infrastructure damage. The well holds infinite water and needs no refills, but the waterboys do. When a worker extinguishes a building, that building cannot be set on fire until some time has passed.
Waterboys are immune to fires and therefore they can pass through it unharmed.
The water pot can be an alternative for the same purpose as the well. While a well is cheaper to site, it only houses one worker, compared to three.