Los Angeles-area businesses could face mandatory water conservation measures this summer as the region’s water wholesaler voted Tuesday to cut supplies and hike rates for the first time in 18 years.

Starting July 1, the Metropolitan Water District of Southern California, which supplies water to 26 agencies serving 19 million people in Southern California, will cut supplies 10 percent from the average usage levels between 2004 and 2006.

The move comes as the state and the entire southwestern United States is in the grips of a three-year drought. The Sierra Nevada snowpack this year was about 80 percent of normal. Meanwhile, environmental restrictions designed to protect endangered fish species have severely limited imports of water from northern California.

The district also voted to raise its rates 8.8 percent and to pass through a 10 percent surcharge on water imported from the State Water Project through the Sacramento-San Joaquin Delta region. The combined 19 percent rate increase takes effect on Sept. 1.

“Up to 19 million Southern Californians this summer will feel the impact of a new water reality that has been in the making for years, if not decades,” said Timothy Brick, chairman of the district’s board.

How much of that impact will be felt by residents and businesses will depend on how local water agencies respond to the cutbacks. Some agencies may be able to supplement Metropolitan deliveries with other sources, such as groundwater supplies, thus offsetting some of the impact.