SAN DIEGO -- Mayor Jerry Sanders Monday declared a water shortage emergency that cements his call for San Diego residents to voluntarily conserve or face mandatory cutbacks down the road.

Sanders said San Diego's water use dropped by 7 percent after he initially called for voluntary conservation in February, but has since "returned to the typical levels."

"In fact, new trends suggest we may be on our way to using more water this year than last year," Sanders said. "This is something we cannot afford and must find a way to avoid."

The city's populous is currently using about 3 percent less water compared to this time last year, he said.

This afternoon, the City Council voted unanimously to formalize the so-called "Stage 1" water shortage emergency, but agreed to have its Natural Resources and Culture Committee hold hearings in September to consider more stringent mandatory cutbacks.

City Attorney Michael Aguirre testified that voluntary water conservation "has not and is not likely to work," and instead urged the City Council to consider a "Stage 3" water shortage emergency. That would force residents to reduce the amount of water they use.

Aguirre delivered a memorandum to the council seeking mandatory water conservation, support for water reclamation and desalination and a temporary moratorium on large developments.

"The ultimate solution to the problem is to increase the supply of water while as efficiently as possible reducing the consumption of water," he said.

Water Department Director Jim Barrett said the earliest the city would have to declare a "Stage 2" water shortage emergency is spring. If that happens, water conservation would become mandatory.

"We do not anticipate having to go to mandatory conservation before the spring," Barrett said. "A lot of that will depend on the weather we get in the winter."

Sanders said he hopes to avoid mandatory water cutbacks.

"We hope San Diegans, as they did at the first part of the year, would voluntarily conserve, as we know they can," Sanders said.

During the council meeting, Sanders said the city attorney's memorandum only "clouds the issue."

"I believe this action to be entirely prudent," he told the council. "I do not agree that we are at a point where mandatory water conservation would be the right thing to do.

"There may be a time, perhaps as early as next year, when more stringent conservation efforts or measures may be called for that judgment should be made thoughtfully and deliberately and not as a knee-jerk reaction," the mayor said.

Sanders' goal is to get San Diegans to reduce they amount of water they use by about 10 percent. He has previously promoted the "20 Gallon Challenge," which calls on all San Diego County residents to reduce the amount of water they use by 20 gallons a day.

He said water conservation is particularly important now during the hot, dry summer months.

"This is a time all of us need to conserve more water and to educate ourselves about the consequences of potential water shortages in the future," Sanders said.

The mayor said his decision to declare the emergency water shortage was necessitated by ongoing drought conditions and a judge's recent ruling that limits the amount of water that can be pumped from the Sacramento-San Joaquin River Delta in order to protect an endangered species of fish.