"There is an apocalyptic side to it," says Jay Famiglietti, a University of California-Irvine professor of earth science and civil and environmental engineering, who also works as a water scientist for NASA's Jet Propulsion Laboratory in Pasadena. "What happens if the drought continues for two or three more years? It starts to become an emergency, disaster scenario."
But it probably would be a slow-motion apocalypse, experts say. Currently, the state gets about a third of its water supply from groundwater, but if the drought continued and the reservoirs started to bottom out, officials would start pumping greater quantities of water from the aquifers to take its place.
The problem is that nobody's quite sure how much groundwater is down there. The best available estimate, according to Famiglietti, is that there's enough to last 50 years at current usage levels. "But if we start draining it at three times the rate, that changes everything," he says. "We'd be looking at running out of groundwater in maybe 15 years."
Before then, though, the difficulty in meeting water demand would probably force state officials to divert water from California's farms to quench the cities' thirst, Parker says. That potentially could be ruinous to farmers, who currently use about 80 percent of the state's water.
"They're a lot more efficient in their water use than in the past, because they've been breeding crops for drought tolerance for years," he says. But it's not clear how much more they could cut back, without going broke and/or having dire effects on food availability and prices.
A severe water shortage also would require cities to import even more potable water long distances, which could lead to conflicts with other parched western states that also lay claim to it. But if that water turned out to be unavailable, Californians might have trouble finding enough to drink -- or to flush their toilets.
While some communities have turned to recycled "gray water" for use in sanitation systems, current building codes and other regulations are hindering that transition, says Famiglietti. That means a water shortage could interfere with the movement of sewage, causing a potentially serious disease risk to Californians.
The horizon for a water apocalypse is still far enough off that California would have time to act. Parker says that coastal cities, for example, could embark upon rush programs to build desalinization plants and recycle more water to reduce demand. Famiglietti says that the aging, mostly low-tech infrastructure for supplying irrigation water to farms could also be upgraded, so that scientists could use satellite data and sensors to more efficiently manage water distribution.
Even so, Famiglietti and others are hoping for intervention from the heavens. They can take some comfort in history: A previous severe drought in 1976-77, after all, was followed by a winter of heavy rains that quickly restored depleted reservoirs.
"If we get lucky and have above average rainfall next few winters everything will be fine," he says. "If we don't have that, then things are going to get really tight."