RIALTO (CBSLA.com) — City officials in Rialto want residents to save more water for a chance to win a Toyota Prius.

Even after this past winter’s flood of rain and back-to-back storms, the city of Rialto faces very low levels of groundwater supplies, according to Rialto Mayor Deborah Robertson. Another three years of average or above-average rain are needed to fully replenish the city’s aquifer, which supplies more than half of Rialto’s water.

READ MORE: Prince Philip Laid To Rest As England Mourns; Prince Harry Attends Funeral

The campaign is part of the Wyland National Mayor’s Challenge for Water Conservation, a program aimed at getting residents to commit long-term to managing water resources.

Rialto isn’t the only California city to lament its low water supplies. While California surveyors measured the state’s heaviest mountain snowpack since 2011, and parts of the state saw 300 percent of normal rainfall in January, forecasters are always quick to temper the good news.

READ MORE: Man Apologizes To Rams Star Aaron Donald For Mistakenly Accusing Him In Pittsburgh Assault

“At this point, it’s not enough,” National Weather Service hydrologist Jayme Labor said in January.

Southern California’s reservoirs are no longer dry, but none of them are anywhere near 100 percent. Lake Casitas in Ventura County had risen to more than 42 percent of capacity, after being at 33 percent in October, before the winter’s biggest storms hit the state.

MORE NEWS: Boy Shot, Killed In Cudahy; Gunman At Large

The annual Wyland water conservation challenge starts on April 1, and lasts throughout the month. Water-savers have a chance to win prizes, including water-saving fixtures and a new Toyota Prius.