CA major reservoirs are well above seasonal average levels, and with runoff will remain that way. We don't need more reservoirs for normal/wet years like this, we need them for droughts like we just had. We should also build at least a dozen desalination plants.
How about the water table? There’s not enough storage. That means run off and it will not last.
California siphons from the Colorado river, the older aquifers but there's a serious need to pump that water underground to replenish the water including central valley and Imperial Valleys.
I don't think California will adopt the Israeli ways of desalination plants and how they make their deserts green which is why replenishing the underground waterways is healthy. It's not a complete answer but it helps.