OAKLAND -- Customers in the East Bay's largest water district should be asked to continue voluntarily reducing their water use 10 percent without mandatory water rationing, the agency's top managers recommend.

To ease shortages, though, the East Bay Municipal Utility District should pipe in an emergency supply of Sacramento River water for its 1.3 million customers in Contra Costa and Alameda counties, managers said.

It would be the first time the district has used the backup supply that has been in the planning for half a century.

The water district's board will consider the plan for coping with drought shortages when it meets at 1:15 p.m. Tuesday in Oakland.

"We think a combination of voluntary savings and the backup supply will give us the storage we need at the end of the season," said Abby Figueroa, a district spokeswoman. "It's important for people to continue to save because we will re-evaluate our reservoir water levels in September."

Managers recommend the district stick with the current program asking customers to cut back 10 percent. In April, customers exceeded the goal with an 11 percent reduction.

Managers also recommend the district pump in 16,000 acre-feet of water in May and June from a joint EBMUD/Sacramento County $900 million water delivery project that was finished three years ago. That's about as much water as EBMUD uses over 32 days.

In fall, Figueroa said, the district would decide if it needs to pump in more water and, if so, how to pay for it.

Earlier this year, district managers suggested a temporary water rate increase of $6 per household per month would be needed to cover the $8 million in pumping costs to deliver the water from Freeport, south of Sacramento.

But on Friday managers said the temporary increase is not needed now because the district can cover the extra costs by dipping into reserves.

Figueroa said those reserves were boosted by selling for $5.6 million a Castro Valley water filtration plant the district no longer needed.

The water board will hold another meeting May 13 to consider the final elements of its drought response -- possibly including whether certain wasteful practices should be banned.

In a written report released Friday, managers predicted the district will have a deficiency in its water storage in reservoirs by Sept. 30. The district will have between 370,000 and 490,000 acre-feet, while anything below 500,000 acre-feet is considered deficient. The district uses about 182,500 acre-feet of water in a year.

An acre-foot is 325,851 gallons, or enough to cover an acre a foot deep in water.

Contact Denis Cuff at 925-943-8267 or dcuff@bayareanewsgroup.com. Follow him at Twitter.com/deniscuff.