The mayor of Los Angeles aims to reduce local water use by 20 percent over the next three years to address a record drought through a mix of voluntary measures for residents and mandatory restrictions for city departments, the city said on Tuesday.

Mayor Eric Garcetti, in an executive order, asked residents in the city of 3.9 million people to limit watering their lawn to twice a week and ordered city departments to reduce watering of municipal lawns.

Garcetti warned that if those and other measures do not meet his goal of cutting the city's water use by 20 percent by 2017, Los Angeles could impose mandatory cutbacks on residents that would include limits on car washing.

The move comes 10 months after California Governor Jerry Brown declared a state of emergency due to a multi-year drought and called for voluntary water use cutbacks of 20 percent.

"Southern California in general has done a remarkable job over these last 20 years of being able to grow substantially without using more water," said Felicia Marcus, chair of the State Water Resources Control Board. "Now this mayor is choosing to take it to the next level, which is a great thing to see."

Already, California officials have announced that water consumption in the state was 11.5 percent lower in August than for the same month the year before.

The drought is expected to cost the state an estimated $2.2 billion this year, along with a loss of more than 17,000 jobs, as farmers are forced to leave fallow some valuable cropland, a report by University of California in Davis scientists found in July.

The city has long offered cash incentives to residents who replace lawns with plants that use less water and other types of landscaping, and Garcetti on Tuesday increased that incentive slightly to $3.75 per square foot (about $40 per sq meter).

He also ordered the city's Department of Water and Power to cut its purchase of water imported from other regions by 50 percent by 2024.

"Our relationship with water must evolve. We cannot afford the water policies of the past," Garcetti said in a statement.