That.. is amenable to technological fixes. As a proof of concept, lets consider the utterly brute force approach: "Fission and desalination":
 Reverse osmosis runs 3-5 kwh/m3, so that works out to..
30000000000 kwh/year? So..
30000000000 kwh/1650000kw*24h*365*0.9 =
3 EPRs running a 90% duty cycle would cover it and spare. If you think manufacturing that much osmosis membrane is unreasonable, add another reactor and the entire thing works using distillation. Water apocalypse averted - This is a small infrastructure program, but as such things go california has done bigger.