Californians have been backsliding on water conservation since the state lifted mandatory conservation for cities and towns earlier this year. North Marin Water District customers in Novato used 12.5 percent less than September 2013.
California remains under a almost three-year-old state-declared drought emergency, despite improved rain and snow since last winter.
Many cities, like Merced and Fresno, have "self certified", meaning they are not held to the strict goals from the state they saw past year.
September's water-savings were better than last month's sagging conservation report, which showed water use shooting up by a third. Officials said they would consider another change if drought conditions persist and water consumption continues to grow.
Californians used 18.3 percent less water in September 2016 than the 2013 benchmark, more than the 17.5 percent they saved in August but less than the 26.2 percent conserved in September of 2015.
The three water suppliers in Riverside all reported daily use in the range of 131 to 194 gallons per person and - like much of the state - didn't save as much water in September as they did a year earlier.
Amid a wet start to California's current rainy season, and some mending of Californians' backsliding ways on conservation, the advice of the state's drought czar: Relax and enjoy the rain, for now. These last few years ... The Governor and several state agencies are inviting developers to use the state's open data to create applications that help save water. "I practically kiss each raindrop", said Felicia Marcus, chairwoman of the state water board.
"We are nearly 400 percent of the normal amount of rain in October here in the north and even the San Joaquin and Tulare regions are well above their averages as well", says Doug Carlson with the California Department of Water Resources.
For some water districts, such as one in the Northern California city of Santa Rosa, the cost-effectiveness of the program is simple: The district will save more money on water going forward, thanks to the lawn reduction, than it spent on the rebates themselves.
Overall, communities statewide conserved 18.3 percent this September compared with the same time three years ago, according to data released Tuesday.
Sponsors of the challenge include the State Water Board, the California Department of Water Resources, California Fish and Wildlife, California Government Operations Agency, and the California Department of Technology.