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Cash-strapped cities are contending with aging, leak-prone water systems that waste trillions of gallons a year and result in damaging breaks.

When forecasters last year warned of a massive El Niño, some Californians held out hope that a single extremely wet year could bust the state’s severe drought.

But a study published Tuesday in Geophysical Research Letters, a journal of the American Geophysical Union, offered support for the argument that state hydrologists have been making for months: It will take several years to recover from the four-year water shortage. Specifically, researchers studied the Sierra Nevada and found that the lackluster snowpack there, year after year, created a sizable water deficit that the state may not recoup until 2019.

Every spring, snow begins to melt throughout the Rocky Mountains, flowing down from high peaks and into the streams and rivers that form the mighty Colorado River Basin, sustaining entire cities and ecosystems from Wyoming to Arizona. But as spring becomes summer, the melting snow slows to a trickle and, as summer turns to fall, all but stops.

Scientists have known for a long time that flow in rivers is sustained by contributions from both snowmelt runoff and groundwater.

When the U.S. Bureau of Reclamation announced last month that the country’s largest reservoir, Lake Mead, had fallen to its lowest-ever level at 1,074ft (327m), the question many asked was: How will it affect one of California’s primary drinking sources?

After all, some 19 million Californians, nearly half the state’s population, receive some part of their water from the Colorado River, which flows into the 80-year-old reservoir created by Hoover Dam outside Las Vegas.