The giant wholesaler that provides drinking water for half the California population has drained two-thirds of its stored supplies as the state contends with a punishing drought, officials said Monday.

Without plentiful rain and snow in coming months, the Metropolitan Water District of Southern California could consider cutbacks to its regional distributors next year. If such limits are approved, that could lead to rationing or cuts for households in portions of Southern California.

"We've gone through a little more than two-thirds of our storage in the last three years," Jeffrey Kightlinger, the agency's general manager, said in a speech in downtown Los Angeles. "Obviously, this it can't go on indefinitely."

At the current rate, billions of gallons in remaining agency reserves could be exhausted in about 18 months. The agency built up those reserves over time as a hedge against the state's periodic droughts.

But those supplies have tightened as the state has experienced a combination of sparse rainfall and unusually warm temperatures — 2014 is on track to be the hottest year in California since record-keeping began over a century ago.

"The situation was have this year is pretty much unprecedented," Kightlinger said.

Gov. Jerry Brown, who declared a drought emergency earlier this year, is urging residents to voluntarily reduce water use.