It was founded in 1926 and is based in San Jose, California, and provides service across multiple local districts, reaching more than 484,900 customers.

[1] California Water Service Company started in 1926 through the acquisition of five separate water systems:[2] The company experienced rapid growth post World War II.

This was a 5.5% annual growth rate during this time reflecting the rapid urbanization of California.

In 2019, a plan for Cal Water's Chico District to purchase water supply from Paradise Irrigation District in the aftermath of the 2018 Camp Fire was cancelled in the study phase.

[7] Cal Water's Willows District installed in 2016 a treatment system to reduce hexavalent chromium in the local water supply using the first strong-base ion exchange treatment system of its type in the United States.