actually it would depend on if your on city water or well water. You can taste the difference in the lack of fluoride and lime or chlorine in the well water. waste water and drinking water come from what is called a "pump station". Back in 1980s I got qualified with a level three certifacate to operate within a class 1 station (Fairfax, Va). If you have no power, it goes to generators, once the generator stop... lack of fuel. No water, and worse of all... no toilets. Those main 8" pipes that your thinking about have different "pump stations" in the city so if a pump station goes out then (manually) it can be "covered" by another pumping station but you might get less water pressure to the area that is affected. 

all states mostly allow people to drill for a well and take care of their own water system. Wells are very simple... it's just a pump that allows water to flow at a avg rate. You might have years before any maintenance would be needed because not much of a strain to the system vs thousands of people flushing toilets, using drinking water, filling pools and watering lawn all at the same time. the maintenance done to those type of systems were ABOVE ground mostly. Water lines to animals, plants, tress and were it was needed. Since this is California... we might need to worry about frostline or broken lines from animals. 

City water / waste will stop in about a week. 

So... the farm could have a pump house. I have a 20 acres but I don't use a pump house on my farm because I don't use alot of water. 

Showers.... Showers are going to be cold after 15-20 minutes of use. With ALOT of people .... that is a big problem. The temp will be around 50 degrees so if you like cold showers then your in for a treat. As for the toilets.... one small problem I can see in the future, I hope that it's a septic tank but you have to remember that the system was built only for those occupying that dwelling. all these people could over load the system in a few days because the grey water will run into the septic tank, it needs time to "recover"...

But this is fiction