Now that we have moved to a 2 floor detached home (also in San Jose) we do not have that issue, and everything is gravity fed.
Larger buildings tend to have multiple independent systems
Alot of suburbs that can't or won't hook into city supplies will sometimes need more active measures to filter their water as well.
Sanitary sewers are heavily dependent on power.
My city runs on surface water, so we have treatment and then pump to storage tanks. You would have to be out for quite a while to run the city out of water, though - the tanks are large.
The aqueduct water is specifically purified by the Los Angeles Aqueduct Filtration Plant. That plant is gravity fed, but it doesn't operate without power.
LA just has the advantage of having mountains in the city, so it's cheaper building more elevated water storage so the capacity lasts longer during power interruptions (which are also not as common or extended as they are in the east). They will still eventually run out if they're not replenished by powered pumps.
You can't have a city of millions of people and have the water be potable from the tap without testing and treatment
> New York City’s water (including drinking water) is unfiltered, making it the largest unfiltered water system in the country. Were New York to begin filtering its water, it would cost the city approximately 1 million dollars per day to operate the filtration plant.
They have hundreds of sampling stations to check daily.
https://www.nytimes.com/2025/05/01/nyregion/nyc-tap-water-qu...
This causes some issues for observant Jews, because the water technically might not be kosher.
https://oukosher.org/blog/consumer-news/nyc-water/
https://www.nytimes.com/2004/11/07/nyregion/the-waters-fine-...
Filtration isn't common.
EDIT: I'm a dork an grabbed the wrong URL. Changed URL to a PDF for lack of better.
A major metro doesn’t treat its tap water? Where on earth did you get that crazy idea?
<old URL deleted>
https://www.nyc.gov/assets/dep/downloads/pdf/water/drinking-...
I'll save some digging: "Even without filtration, the water is carefully treated to reduce the risk of harmful microorganisms."
Tap water is treated (UV and chloride disinfecting), but is largely not filtered: https://en.wikipedia.org/wiki/New_York_City_water_supply_sys...
The untreated NYC water has tiny crustaceans in it, which make it not Kosher, which is why thee bagels from a Jewish deli in NYC are so good. Go figure.
https://newsfeed.time.com/2010/08/31/drink-up-nyc-meet-the-t...