NorCal, including Sacramento, is on the western side of the Sierras.
So unless they planned on pumping the water over/under the mountain range that surrounds it in every direction except for towards LA, that water was never available for any NorCal city to use.
https://en.wikipedia.org/wiki/California_Aqueduct
Would be interesting to see the relative amounts of use by LA and by agriculture in the Central Valley though.
But SoCal isn't only LA. LA itself gets a bit less than half of their water from MWP, which manages the water from the SWP and the Colorado. About the same amount it gets from the the eastern Sierras. These are supposed to drop to ~10% of LA's water supply as recapture/recycling projects complete.
Or computed the other way around, LA only has rights to ~20% of the water managed by MWD. Of course water supply, distribution, and rights are all blended and traded around all the time, but generally speaking it's not "LA" using up that water from NorCal, the consumption is significantly more from the cities and farms that came after.
https://www.ppic.org/publication/water-use-in-california/
tl;dr: Urban water use is tiny. In NorCal, the vast majority of the water flows unimpeded to the sea. In the Central Valley, most water is used for agriculture. Agricultural water use in any one of the 3 major basins in the Central Valley is more than all urban areas in California combined. Unsurprisingly, urban use is the primary one in the SF and LA areas, but the absolute totals are very small compared to total CA water supplies.
But really, California (and really the entire Western US) needs a water rights governance overhaul. Right now the focus is all on urban water use, which is practically negligible compared to the agricultural water rights usage.
We created the miracle on the desert, and billions were made in real estate.
Meanwhile, San Francisco drinks clean glacier water that a valley in Yosemite was destroyed to provide this and they refuse to repurpose a downstream damn that has enough capacity to do it.
Physician, heal thyself.
California has insufficient water storage to meet demand, it’s not like we have huge dams lying around that we leave empty when there is water available to fill them.
You might be referring to Don Pedro dam - but we are already filling that up (modulo what we need to keep empty for flood control). SF has some contractual right they could possibly exercise to water in Don Pedro but that doesn’t magically result in California’s water supply being held constant if we stop storing water in the Hetch Hetchy. If SF gets the Don Pedro water, that means someone else that was going to get it is deprived.
Now, you could argue that the state can get by with lower storage because ag needs to consume less or more groundwater recharge or whatever, but that’s a different question.