San Francisco and Oakland each approved a 45-day pause on data center development Tuesday, giving city officials time to study the facilities’ effects on water supplies, electricity demand, air quality and surrounding neighborhoods. San Francisco’s Board of Supervisors voted unanimously to halt new data center projects and expansions of existing facilities, effective immediately. Oakland’s City Council also voted unanimously for a moratorium on new approvals. The cities are the first in the Bay Area to adopt such pauses. In San Francisco, the Planning Department will use the review period to assess environmental and land-use impacts and develop a clearer definition of what qualifies as a data center. The Planning Commission is expected to hold a hearing on the findings when the initial pause ends. The moratorium could be extended for as long as 22 months if the city finds significant environmental effects while it considers longer-term rules. District 10 Supervisor Shamann Walton introduced San Francisco’s measure last month, citing environmental concerns and limited community input on proposed projects. Data centers are concentrated in District 10, an area that has historically borne a disproportionate share of the city’s industrial pollution. Supervisors Connie Chan, Jackie Fielder and Cheyenne Chen co-sponsored the measure. The pause puts a planned expansion at NOVVA’s 7.6-acre Bayview data center on Paul Avenue on hold. The project was slated to increase the facility’s power capacity from 9 megawatts to 36 megawatts by 2028. The moratorium does not, however, halt separate utility work: a reported upgrade to PG&E infrastructure near the site is not covered by the city measure. Other San Francisco proposals include a permit application for a 160,000-square-foot data center on Michigan Street in Dogpatch and proposed facilities in District 6, including a SoMa project reportedly being developed by Amazon. Oakland’s review will examine potential effects on water, the electrical grid, air quality and other infrastructure. Residents and activists raised concerns at a City Council meeting, including about the water some data center cooling systems can require. Dr. Elizabeth Dougherty warned the council about increased demand on Oakland’s water supply from the Mokelumne River and possible effects on ecosystems upstream in the Sierra Nevada. Councilmember Carroll Fife, who sponsored Oakland’s measure, has also criticized developers’ use of nondisclosure agreements, saying they can limit what residents and officials learn about proposed projects. One development under discussion is Behring Companies’ plan for a data center on the ground floor of a building near 20th and Franklin streets, with artificial-intelligence research planned for upper floors. Mayor Barbara Lee said the pause would give residents a chance to shape the city’s approach to future projects. Fife has scheduled a community meeting about data centers for 10 a.m. Oct. 24 at Beth Eden Baptist Church in West Oakland. The local pauses come amid broader debate over data center growth in California. Other Bay Area communities, including Pittsburg, Oakley and Gilroy, have faced opposition to proposed facilities, and Gov. Gavin Newsom signed several state laws regulating data center development last month.