Flagstaff water commission presses for strict rules on data-center cooling, favors air-cooled baseline

The Flagstaff City Water Commission on March 19 reviewed a proposed zoning-text amendment that would add a definition for "data center," limit the land use to heavy-industrial zones by conditional use permit and attach specific mitigation standards for noise, landscaping and water use.

Tiffany Antl, the city's zoning code manager, told the commission staff are not trying to "create the opportunity for data centers in our community" but to "create specific standards for something that's already allowed." The draft would require baseline noise studies, site-planning and architectural standards, screening of mechanical and electrical equipment, and a 200-foot setback where data centers would abut residential zoning under Planning & Zoning’s recommended language.

The proposal includes a robust CUP submittal checklist: estimates of peak, average and annual water and wastewater demand; identification of the water source requested (potable or reclaimed); documentation from utilities that sufficient power and water exist; an assessment of wastewater constituents; and a preferred (but not mandatory in zoning) goal of 100% non-potable/recycled water for non-potable uses.

Water-services staff framed the department’s existing review process as an important safeguard. Aaron Young, water-resources section director, said large users trigger a WHISA (water and sewer impact study) "based on peak hourly demand over 10 single-family homes," followed by system-capacity and industrial-discharge reviews. He told commissioners staff can require upgrades or deny service if capacity is lacking.

Commissioners pressed staff on cooling-system language. Tamara, the water conservation program manager, read an expert note explaining that even a closed-loop chilled-water system often requires a heat-rejection mechanism — "most commonly a cooling tower" — and that the heat-rejection side typically consumes significant water through evaporation and blowdown. That technical point undercut a simple assumption that "closed-loop" alone eliminates sizable water use.

Staff presented three policy options: an air-cooled-only rule (prohibit water-based heat rejection), a performance-based standard with submetering and annual reporting, or a hybrid approach (air-cooled baseline with narrowly defined exceptions). Tiffany told the commission an outright ban had been drafted at Planning & Zoning's request but was not staff's preferred approach. She warned of legal vulnerability under Arizona property-rights law (Prop 207) if the city were to reduce an allowed land-use value without careful justification.

Several commissioners said an air-cooled baseline would be the simplest and most enforceable approach while water-services develops a more detailed large-water-user policy. Commissioner Emily Melhorn (participating remotely) cautioned that limiting facilities to air cooling "would limit the size of the data center" and recommended submetering and stronger recycling/performance metrics if water cooling is ever allowed.

Next steps: staff will refine technical language — particularly cooling-system and water-efficiency provisions — gather additional expert wording, and carry feedback to the Planning & Zoning Commission's upcoming public hearing. The zoning amendment, Planning & Zoning public hearing and subsequent City Council consideration will determine whether and how the changes become code.