California has at least 270 data centers and no state requirement that any of them report how much water they use. The governor vetoed a bill that would have changed that, signing instead a law to study data center electricity consumption. The asymmetry in what California chose to measure and what it chose not to measure reflects an industry lobbying position, not a regulatory judgment about which resource is more at risk.
The water question in California is legitimately complicated. The state has no standard definition of what counts as a data center, no centralized registry, and no consistent methodology for measuring cooling water draw across facilities with very different thermal architectures. One operator estimated its annual facility water use at 2.8 acre-feet. A planned facility in the Imperial Valley was estimated to use 750,000 gallons per day, roughly 840 acre-feet annually. The gap between those two numbers reflects real differences in facility size, cooling technology, and climate, but it also reflects how little standardization exists in how operators account for water consumption.
At least 270 data centers in California (no definitive count due to no standard definition). No state water disclosure requirement after governor's veto. Reported facility water use: 2.8 acre-feet/year (small facility) to 840 acre-feet/year (large planned facility). On hot summer days, a large data center can exceed 1 million gallons of water withdrawal per day. Some facilities under construction have been allocated up to 8 million gallons per day.
On hot summer days, a large California data center can withdraw more than 1 million gallons of water. Some facilities under construction have received water allocation permits of up to 8 million gallons per day. Aggregated across the cluster of facilities that Silicon Valley and the Central Valley represent, the water draw is already happening. The problem is that without consistent disclosure requirements, neither regulators nor the public has a reliable accounting of the total.
The governor signed a law to study electricity impact while vetoing water disclosure. That sequence is instructive. Electricity consumption became the lead regulatory concern because utilities have metered data that makes the numbers visible. Water consumption from cooling towers does not appear on a public meter in the same way, which makes it easier to defer. The absence of data is not evidence of a small problem. It is evidence of an unmeasured one.
Water-cooled facilities draw more from the municipal supply than air-cooled ones, but air cooling at AI rack densities is no longer technically viable. Physics settled the air versus water question already. The question is which water cooling architectures California should require or incentivize for new construction and major retrofits.
Closed-loop systems with dry heat rejection use a fraction of the water that open evaporative systems consume. A facility designed around direct-to-chip liquid cooling with an air-cooled heat exchanger loop can achieve near-zero consumptive water use. That is the architecture California should be specifying in permit conditions for new data center construction, particularly in regions already under water stress: the Central Valley, Southern California, the Imperial Valley. The governor's veto of the disclosure law makes it harder to build the evidentiary record that would support that kind of permit-stage specification.
Big Tech blocked the California data center rules that moved through the legislature in 2025. The argument was that disclosure requirements and prescriptive cooling standards would make California less competitive with Nevada, Texas, and other states offering lower regulatory friction. That argument has a limited shelf life. California is where the engineers live. It is where the largest concentration of AI companies is headquartered. It is also a state with documented water supply constraints that are going to get worse. The water disclosure veto delays a reckoning, it does not eliminate one. When California eventually mandates water reporting, and it will, operators who built without considering the regulatory trajectory will find themselves retrofitting cooling architectures under compliance pressure rather than on their own timeline.