SAN DIEGO -- According to a new report by the research group Equinox, researchers said if the county does not diversify with options such as recycled water, local residents could eventually be forced to use half as much water in two decades.

The group ranked the county's water sources on seven different factors, from reliability to cost to availability.

Imported water, which is 80 percent of the county's water supply, received the lowest overall score.

Researchers expect the price of imported water to climb drastically over the next two decades. They estimate it will rise about seven percent every year because of many factors, including fixing crumbling infrastructure, the threat of earthquakes and looming legal disputes of water rights.

"Importing water is not optimal or sustainable," said Marion Paul, the executive director of the Equinox Center.

Desalination of seawater also scored very low.

"I think the big surprise was the amount of energy desal needs for conversion," said Paul. "It's twice that of recycled water for example."

Researchers said energy costs may make desalination too expensive for the future, while county officials continue to defend desalination.

"We still have studies coming out that will look at cost, but we know they have desalination has the highest reliability. It's a piece of the puzzle," said Bob Yamada, the water resources specialist for the County Water Authority. "We have a goal of 60 percent imported water by 2020. We will get there."

Both Yamada and the researchers agree that other options are essential.

"Water recycling is a key component," said Yamada.

It would also include recycling wastewater for landscaping and drinking water.

Another conclusion from the research was that conservation is critical and if the county does diversify, tough restrictions are likely.

The report was put together by Equinox Center and Fermanian Business and Economic Institute.