San Diego County businesses and residents, please turn off your irrigation systems for the near future. Mother Nature will do the watering this weekend.

Moderate to heavy rains are expected to return to the region late Friday and continue through Saturday, according to the National Weather Service.

Forecasters have issued a flash flood watch for that period, with an inch of rain per hour possible. Significant flows are expected in the Santa Margarita and San Luis Rey rivers.

The San Diego County Water Authority is asking residents and businesses to take the irrigation hiatus to conserve the area's water supply. Forecasters expect a storm to arrive late Friday and last until Sunday, the water authority said in a Thursday advisory.

"Following a significant storm, irrigation systems can remain off for several weeks," the authority said.

While rainfall so far this year is slightly above normal, just 5 to 7 percent of the county's total water supply is from local rainfall, said the water authority. The rest is imported, and getting water here from the critical Sacramento River delta is difficult, due to regulatory restrictions.

The water authority estimates that a one-week pause in irrigation could save 2,000 acre-feet of water. That's enough to supply 4,000 average families of four for one year, the water authority says.

"Restrictions activated in late January to protect salmon are currently causing the loss of 10,000 to 12,000 acre-feet of water every day to the State Water Project and federal Central Valley Project combined," the water authority said. "Even greater water losses are expected if delta smelt protections are implemented. These restrictions would cut pumping by more than 50 percent below the already-reduced levels."

More water-saving tips are available at: http://www.20gallonchallenge.com.

Call staff writer Bradley J. Fikes at 760-739-6641. Read his blogs at bizblogs.nctimes.com.