The statewide educational campaign is in response to last month's declaration of a drought emergency by Gov. Jerry Brown.
In his proclamation, Brown said the state's rivers and reservoirs are at alarming levels and ordered Californians to cut back at least 20% of their water use.
Brown also ordered state agencies to prepare for water shortages and launch water conservation campaigns.
"Caltrans has taken action to sharply restrict water usage," Caltrans Director Malcolm Dougherty said. "Using our highway message signs, we are asking California's 24 million drivers to join us in this important effort."
Many of the electronic signs will read: Serious drought. Help save water.
The messages will only be activated when there are no emergency or traffic safety messages or
State transportation officials hope the electronic signs will help increase awareness about the Save Our H20 campaign, which is being spearheaded by the Department of Water Resources.
Caltrans officials said that, in addition to the signs, it is cutting back irrigation activities by 50% and won't wash vehicles except when necessary for safety reasons. The agency, which is responsible for 30,000 acres of irrigated landscaping, said it would delay new landscaping projects, postpone highway planting and cease using water irrigation in areas severely affected by the drought.