Californians reduced their water use by a hefty 29 percent in May, the biggest monthly decline since Governor Jerry Brown called for a mandatory cut due to severe drought conditions, according to figures released Wednesday by the State Water Resources Control Board.

"The numbers tell us that more Californians are stepping up to help make their communities more water secure, which is welcome news in the face of this dire drought," Felicia Marcus, chair of the State Water Resources Control Board, said in a statement. "That said, we need all Californians to step up -- and keep it up -- as if we don't know when it will rain and snow again, because we don't."

The report followed several months of tepid conservation. Monthly residential water savings were 28.9 percent in May, compared to May 2013, which is a significant increase from the 13.6 percent water savings in April, compared to April 2013, the water board said.

The data is self-reported by more than 400 California water departments and includes residential and business consumption. All regions of the state showed improvement.

Between June 2014 and May 2015, approximately 237.3 billion gallons of water were saved, as compared to the same time period for the previous year. This is enough water to supply approximately 2.38 million Californians for one year.

In May, California residents used 87.5 gallons per capita per day, three gallons per day less than the previous month.

California is in a four-year drought and the water board has assigned each community a mandatory conservation target between 4 and 36 percent, depending on how much water residents used last summer.

Cities that don't meet these targets face fines or state-imposed restrictions on water use. But some have complained these targets are unfair because they do not take into account water savings before the drought or how secure local supplies are.