Heavy rain - with more expected this weekend - muddied roads and tied up traffic but failed to avert mandatory water rationing starting Friday in California's two most populous regions.

Los Angeles residents have to cut water use by 10 percent, while restrictions in Marin County north of San Francisco are so tight just taking two 5-minute showers might use up the daily limit."My lawns are going to die. And you can't flush every time," said Pat Winterson of Mill Valley, one of hundreds who picked up a water conservation kit at the Marin Municipal Water District headquarters this week.

The water conservation mandates go into effect despite the state's first major rainstorm this year. Los Angeles got 3 inches in two days and parts of northern California got around 1 inch.

The storms were blamed for power outages and dozens of fender-bender traffic crashes caused by hubcap-deep water and roads awash with mud.

Southeast of Los Angeles, a tornado damaged 46 homes, uprooted trees and hurled an office shed onto a freeway Thursday as it smashed its way across Orange County. No injuries were reported, police said.

Several storm systems were expected to dump even more rain this weekend.

But the rain was expected to do little to ease the drought, said Doug Priest, director of the state Drought Center in Sacramento.

"If we were to get 200 percent of our normal rainfall during the rest of the wet season - the next 40 or 50 days - we would only get up to about 50 percent" of normal for the season, he said.

Los Angeles relies on Sierra Nevada snowpack for 70 percent of its water, and the Marin Municipal Water District on seven reservoirs. All sources are at dramatic lows.

A January survey by the Department of Water and Power, which serves 1.3 million people, showed the snowpack in the eastern Sierra watershed, 250 miles north of Los Angeles, was only 13 percent of normal.