"We're really in a very, very difficult situation," Jay Famiglietti, a scientist at Nasa's Jet Propulsion Laboratory, told CNN. If reservoirs run dry, California will be reliant on groundwater, also at historic lows. Overuse by Central Valley farmers has caused ground to slump 0.3 metres per year.
Famiglietti fears aquifers will run dry before a 2014 law, requiring local bodies to sustainably manage water, takes effect. "The future of California is not quite apocalyptic," he said, "but we'll have some major changes."
The most important cultural shift for the state's 38 million people is that they mostly live in an arid, or semi-arid, environment - some of it desert - and that a century's profligate water use has been an aberration. The average Californian household uses 530 litres per person, per day. The Auckland equivalent, in a country with far higher rainfall, is 176 litres.
This January was the driest in California since records began in 1895, reinforcing fears of a mega drought. Last year the Journal of Climate said the region faces a 20 to 50 per cent chance of a drought lasting upwards of 35 years. Deeper droughts, driven by soaring population, business and farming intensification, urbanisation and climate change, are a global challenge. The United Nations predicts the planet will face a 40 per cent water shortfall by 2050.
The question galvanising decision makers in America's most populous state - the world's seventh largest economy with a US$2.2 trillion GDP - is how California will cope with what may be an exceedingly dry future. And, in a climate change world, where California goes may hold lessons for us all.
"It will require a sea change on how we manage and use water," says Heather Cooley, water programme director at the Pacific Institute, a think tank.
"The old thinking was to go beyond the next mountain to the next river and import water." The result was a vast, interconnected state and federal infrastructure that transferred inexpensive water to farms and cities.
The cheap era is over. It is unsure if costly water transfers can sustain lucrative but thirsty crops, like almonds and pistachios. Farmers lost US$2.2 billion in 2014. Less water may mean fallowing more land.
Money must also be found, most likely from higher user fees, to earthquake-proof neglected pipes and canals. The "Big One", a slip on the San Andreas Fault, could breach the century-old Los Angeles Aqueduct, which channels water from the Owens Valley to Los Angeles.
Lucy Jones, a United States Geological Survey seismologist, told the Los Angeles Times a monster quake is "the biggest single vulnerability we're facing in Southern California".
The state has contingency plans for quakes, but seems blindsided by the threat of prolonged drought. Cooley says California needs a better water strategy than just hoping it will rain. Last November a water bond earmarked US$2.7 billion for storage. Dams are the most expensive option, and agribusiness would have to stump up billions as the bond only covers public use. The cheaper alternative is to replenish depleted aquifers.
Rationing is the new normal, as agencies like the Metropolitan Water Board of Southern California consider slowing the flow. Higher water bills, retrofitted pipes, grey water, drought-resistant gardens and desalination - a US$1 billion San Diego plant will produce 189 million litres a day, 7 per cent of need, in 2016 - all toll the bell for the hosing of summer lawns.
Improving efficiencies are also low-hanging conservation fruit, a goal that can draw on the state's record of innovative, high-tech ingenuity. But, ultimately, California needs a major rethink, rejecting the notion nature can be "tamed" for human benefit. This will mean reversing a century of federal activity, so that wetlands are re-wilded and water soaks into aquifers rather than running to the sea. In a climate change world, stalked by drought, subjugating economies to the environment may be the best hope.
