Mostly everything except water availability are determined not by zones but by whether or not they are visited by a particular worker (e.g. engineering to stop buildings from collapsing or prefecture to stop crime and fire). That means the little prefect or engineer has to physically walk by the building in order for that building to be considered serviced. This can be nice because they themselves set up routes that allow for more complex patterns of availability for that service, but it can also be very aggravating because the AI worker may have a shop right next to another building and yet never seem to visit it. This means you have be very careful how you construct your roads and furthermore, you may have to micromanage your worker's paths literally cutting the road so they turn left instead of right and then re-anealing said road back together. It is one of the more aggravating parts of an otherwise really good game.