In the latest sign that California's historic drought is having a worsening impact on Silicon Valley, the region's largest water provider is putting in place unprecedented cutbacks this spring on cities, farmers and its own efforts to recharge groundwater supplies.

Because of the lack of rain, the Santa Clara Valley Water District last week alerted seven cities and companies that provide water to about 1.5 million people that it will provide only 80 percent of the treated drinking water they have requested through the rest of the year.

"They understand the challenge we have right now," said Angela Cheung, a deputy operating officer at the water district. "This is the best we can do, given the circumstances."

That type of reduction has never happened before, district officials say, at any time going back to the 1960s.

The agency also will soon stop farmers, golf courses and rural residents from accessing water from creeks and public pipelines, mostly in South County.

The 20 percent urban cutbacks do not mean that the affected cities -- which include San Jose, Mountain View, Sunnyvale, Cupertino, Milpitas and Santa Clara -- will run out of water. Rather, they will be forced to make up the 20 percent loss of their supply by pumping more groundwater, urging residents to conserve this summer and using other sources, such as supplies they may receive from San Francisco's Hetch Hetchy system.

Still, the news that the spigot is being tightened comes as a stark reminder of how bad the drought has become.

"This is the third year of a drought. It's been a really warm winter," said John Tang, a spokesman for the San Jose Water Company, a private company that delivers water to 1 million residents in and around San Jose.

"It's definitely a cause for concern. We want people to use water judiciously and heed the call for conservation so we can make it through this year."

Tang said San Jose Water will make up its 20 percent reduction in water district supplies by pumping more groundwater from its roughly 100 wells around the county and by asking for conservation. The company has drawn up new rules for watering lawns and landscaping only at night, and addresses ending in even numbers water on even dates and odd numbers water on odd dates. But for now, the company will not impose fines on violators, only warnings, and the plan cannot take effect until approved by the California Public Utilities Commission.

Dry, dry, dry

Even with modest showers expected this week -- up to roughly half an inch this week -- San Jose has received only 4.76 inches of rain since July 1. That's just 37 percent of normal. The Sierra Nevada snow pack, a key source of California's water, was 24 percent of normal on Monday.

And for the first time in its 54-year history, state officials announced last month that the water district and other agencies would be receiving no water from the California State Water Project, a series of dams and canals that pump water through the Sacramento-San Joaquin River Delta to farms and cities from the Bay Area to San Diego.

With less water coming in, the district says, it must begin taking tougher actions. Already it has asked everybody in the county to cut water use by 20 percent and has ramped up public information campaigns.

The district also will cut the amount of water it puts back into underground aquifers by 75 percent -- to about 25,000 acre feet this year, instead of the 100,000 acre feet that is banked in most years.

Farm impacts

In the change that has caused the largest political stir, the district on Friday sent letters to property owners who receive untreated water from creeks and pipelines announcing that they will be cut off entirely from those sources on May 1.

There are 99 such property owners. Of those, 32 are farmers, seven are golf courses and most of the rest are rural homeowners. Together, they make up a small amount of total water use in Santa Clara County -- 3,477 acre feet, or about 1 percent. But many have used the water as far back as the 1970s when they signed agreements with the water district to allow pipelines to run across their property on the condition that they could draw water from them.

Now, some, farmers in particular, are unhappy.

"I already have drip tape out there, I have rows planted, I have thousands and thousands of dollars invested," said Tim Chiala, co-owner of George Chiala Farms in Morgan Hill. "I don't see cities cut to zero. Why is everything falling on agriculture?"

Chiala's family grows garlic, peppers and string beans on 1,300 acres in Morgan Hill, Gilroy and Hollister. On 300 acres in Morgan Hill, it draws water from a district pipeline that now will be cut off. The family will make up the difference by pumping more from three wells on the property, he said, a fall-back position that farmers across the state are using as a last resort to stay in business as surface water supplies dwindle.

Water district officials say they are trying to preserve as much water for people in cities to drink in case the drought drags on into next year and, as a result, the farmers must have this supply cut and go to their wells, something their permits with the district allow for in drought years.

"We're fine to deliver it in normal years, but in very dry years like this, they need to have other supplies," said Joan Maher, a deputy operating officer for the water district.

Paul Rogers covers resources and environmental issues. Contact him at 408-920-5045. Follow him at Twitter.com/PaulRogersSJMN.