Though Contra Costa County is bordered to the north by the Sacramento/San Joaquin Delta, the quality of that water has been a concern since the area was first settled in the 1870s. Concerns about rising salinity from the San Francisco Bay is one of the reasons the Contra Costa Water District was formed in 1936.
Though the District pumped most of its water from Delta locations upstream near Oakley, salinity continued to be a problem. During the drought in 1977, the driest year on record in California, salinity levels exceeded public health limits and water was rationed by CCWD and other Northern California water districts.
The District considered a number of ideas, and in 1988 voters approved authorization funding of the $450 million Los Vaqueros Reservoir project. The measure won with 68 percent of the vote. After years of design, construction began in 1994.
The reservoir was completed in 1998, and could store up to 100,000 acre feet of water.
In 2012, it was expanded by the water District and now has a capacity of 160,000 acre-feet. It is now the largest reservoir in the Bay Area.