The mandatory reduction includes residents and businesses. Commercial water customers are required to reduce irrigation by 30 percent for landscaping. It also bans the washing of cars or boats without a nozzle, and prohibits the washing of outdoor surfaces unless necessary for health and safety.
Roseville says outdoor irrigation accounts for more than half of a typical home's water use, and says reducing that is the quickest way to reach the 20 percent goal.
The city gets most of its water from Folsom Lake, which is extremely low due to the drought. Earlier this year, the city turned on its groundwater wells in order to conserve water from the lake, but turned them off this month after more rain and snow fell in Northern California. The city of Sacramento has also implemented a mandatory 20 percent reduction.
While Roseville is calling the reduction "mandatory," water customers will not be hit with a surcharge or penalty if they do not meet that target.
Roseville, the largest city in Placer County, operates its own utility, which serves most of the 127,000 residents. Officials backtracked on a February proposal that would have used surcharges to compel reductions
Water conservationists criticized Roseville's approach, saying that without an enforcement or penalty structure, customers were unlikely to heed the call. But city leaders expect that education and outreach will translate into cutbacks.
The Associated Press contributed to this report.
California Communities Respond To Drought
The drought can be blamed for a number of problems and the latest is a major decline in the duck population. A new survey shows lack of rain has led to poor habitats.
UPDATED: 6:45 p.m. - Containment has grown to 29 percent, and acreage burned to 17,622. Crews on the Washington Fire, three miles south of Markleeville, took advantage of light winds to increase containment.
California water regulators are again ordering some water rights holders to stop diverting water from rivers because of the drought. The order includes some rights for the city of San Francisco.
CAL FIRE increases staffing as the forecast of dry lightning and thunderstorms raises wildfire risk in northern California and western Nevada.
The Washington Fire has burned within about three miles of the small town of Markleeville in Alpine County. But crews have made protecting the community a priority.