The company said it is working "around the clock" after an Iranian-linked group claimed it hacked its systems.
Iranian state media displayed what appeared to be a customer's bill as proof of the breach.
The group, known as Handala, reportedly stopped short of cutting off water but claimed it could.
In a statement, Cal Water said its "...preliminary findings indicate that there are no known operational disruptions to our water and wastewater systems, including the billing platform." The company added that "...it maintains a number of cybersecurity, water system security, and water quality assurance measures..."
The alleged hack comes amid ongoing tensions in the Middle East. Iranian state media tied the cyberattack directly to the war in Iran, stating it was in retaliation for U.S. strikes.
U.S. Central Command said those strikes, on June 10, targeted surveillance capabilities and communication systems.
Iranian officials said the U.S. actually struck reservoirs, cutting off water to 20,000 residents.
Republican Congressman Vince Fong called the cyberattack "a wake-up call," writing in a post on X that "adversaries are actively targeting our water infrastructure, hospitals, and other soft targets in our backyard."
Fong confirmed he is in communication with the Department of Homeland Security. Cal Water said it will "closely collaborate with our federal and state government partners."
At the Cal Water office in Visalia, activity was quiet on the holiday, with only a few customers arriving to pay bills in person.
One couple said they were not aware of the reported hack but noted that cyberattacks are becoming increasingly common.
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