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Arizona’s housing growth just ran into a question that’s bigger than any one subdivision: who gets to change the rules for water, and how? We sit down with Phoenix water law attorney Michele Van Quatham to unpack a trial court ruling in Home Builders Association of Central Arizona v. Arizona Department of Water Resources, a case that turns on the 100-year assured water supply program and the power of agencies to shift policy without formal rulemaking.

We walk through how a developer typically qualifies for a 100-year water certificate in the Phoenix Active Management Area, including the groundwater “physical availability” analysis, hydrology studies tied to specific wells, and the 1,000-foot depth-to-water standard. Then we dig into the conflict sparked by the new Phoenix AMA groundwater model and the resulting pause on new determinations. The key legal issue is administrative procedure: the court finds that expanding the “affected area” to the full regional model functions like a new rule of general applicability, which requires public notice and the Arizona rulemaking process.

From there, we connect the courtroom fight to real-world water policy and planning. We discuss a second lawsuit challenging a program that effectively demands 125% to 133% of water supplies, the limits of Colorado River and Central Arizona Project water for replenishment, and why “new water” quickly becomes expensive. Finally, we explore practical paths forward, from advanced water reuse and direct potable reuse to desalination concepts and the complicated water footprint of data centers once energy and cooling are counted. If this conversation helped you see Arizona groundwater management in a new light, subscribe, share the episode, and leave a review.