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Arizona Joins Nevada’s Colorado River Lawsuit to Fight Federal Water Cuts

Phoenix-area water supplies face two phases of federal cuts unless Arizona and Nevada win in court together

Published Oct 18, 2026

Aerial photograph of Lake Powell and Glen Canyon Dam on the Colorado River showing dramatically low water levels with a prominent white bathtub ring on canyon walls, the concrete arch dam visible at lower right, and the reservoir winding into the distance through red sandstone desert terrain — Lake Powell and Glen Canyon Dam on the Colorado River, showing a stark white bathtub ring on the canyon walls — a sign of the prolonged drought and declining reservoir levels that prompted the federal plan now being challenged in court. (aerial photo)

The short version

Without the Lower Basin Agreement, CAP's Colorado River supply would be cut 77% over 2 years.
Arizona loses 760,000 acre-feet per year under the federal plan — roughly 250 billion gallons annually.
Federal cuts hit 20% through 2028, then could reach 40% after that, per the lawsuit.
CAP serves nearly 6 million people across Maricopa, Pinal and Pima counties.
Nevada originally filed Aug. 24, 2026 — 3 days after Interior Secretary Burgum signed the final plan.

Arizona officially joined Nevada’s lawsuit against the U.S. Department of the Interior on Oct. 16, 2026, aiming to block a federal Colorado River plan that would cut the state’s water supply by roughly 27% — and potentially much more after 2028. For the nearly six million people who rely on Central Arizona Project water across Maricopa, Pinal and Pima counties, this lawsuit is the main line of defense.

Your CAP water, your water bill, and what’s actually at risk

If you live in Phoenix, Tucson, or most communities in between, your tap water travels through the Central Arizona Project. The CAP is the largest water delivery system in Arizona. The Colorado River is its source.

The federal plan being challenged in court would cut Arizona’s Colorado River allocation by about 20% through 2028. After that, the lawsuit says cuts could reach 40%. That second phase is the bigger worry.

Arizona, California and Nevada reached the Lower Basin Agreement in May 2026. Without it, the CAP’s Colorado River supply would be cut by 77% over the next two years. The agreement is holding that threat back for now.

What does that mean on the ground? Greater reliance on groundwater, which is more expensive to pump. Potential rate increases as utilities pay more to find and treat alternative supplies. Long-term uncertainty for farmers, homebuilders and businesses across Maricopa, Pinal and Pima counties.

No one can say yet whether your water bill will go up, or by how much. But ADWR Director Tom Buschatzke said the federal framework “could result in cuts to the state apportionment that would devastate Arizona’s economy.” That is the official position of the state agency that manages Arizona’s water supply.

A bathtub ring marks where water once stood on a Colorado River reservoir. Low levels like these drove the federal plan now being challenged in court. (aerial photo)

What Arizona just did — and why it did it Friday

Governor Katie Hobbs and the Arizona Department of Water Resources announced Friday, Oct. 16, 2026 that Arizona has intervened in Nevada’s existing lawsuit. The state is not filing a separate case — it is joining as a party to the action Nevada already started.

Nevada moved fast. The Nevada Attorney General, the Colorado River Commission of Nevada and the Southern Nevada Water Authority filed the lawsuit on Aug. 24, 2026. That was just three days after Interior Secretary Doug Burgum signed the final federal plan on Aug. 21.

Arizona had been building toward this. Lawmakers set aside funds for potential legal action. ADWR retained outside counsel. The City of Phoenix retained its own attorney in August. The Central Arizona Project’s governing board authorized its attorneys to pursue legal action in September. By the time Governor Hobbs announced the intervention Friday, four separate Arizona actors had already taken formal steps to fight the federal plan.

The federal plan: how Arizona became the biggest loser

The federal plan cuts Colorado River supplies to all three Lower Basin states — Arizona, California and Nevada. Arizona takes the hardest hit by far.

Arizona loses 760,000 acre-feet per year. That is nearly 250 billion gallons annually. It represents roughly 27% of the state’s full Colorado River allocation.

The four Upper Basin states — Colorado, New Mexico, Utah and Wyoming — are not required to give up any water under the federal plan. That asymmetry sits at the center of Arizona’s legal argument.

The Colorado River winds through desert mountains. Nearly 6 million residents across Maricopa, Pinal and Pima counties depend on this water through the Central Arizona Project. (aerial photo)

Upper Basin vs. Lower Basin: the fairness argument driving the lawsuit

The law of the river is the set of compacts, court decisions and federal agreements that govern Colorado River water. A core requirement: Upper Basin states must deliver a minimum amount of water to Lake Mead each year.

The lawsuit argues the federal plan ignores that obligation. The federal government is placing nearly the entire conservation burden on Lower Basin states. Arizona absorbs the largest single cut of anyone. The Upper Basin gives up nothing.

Buschatzke put it plainly: the plan “ignores basic elements of the law of the river.”

A 20% cut through 2028 is painful but manageable, especially with the Lower Basin Agreement in place. A 40% cut after 2028 is a different problem. Arizona cities, farms and tribes would need replacement water supplies that do not currently exist at scale.

The Lower Basin Agreement: what it is and what it is holding back

In May 2026, Arizona, California and Nevada agreed to conserve more than 3.2 million acre-feet of water in 2027 and 2028. The goal was to stabilize the river and avoid deeper federal cuts.

That agreement is doing real work right now. Without it, the CAP would face a 77% cut to its Colorado River supply over the next two years. Governor Hobbs said Arizona would keep working with Nevada and California to carry out that agreement. At the same time, Arizona is suing the federal government over the plan it imposed.

The lawsuit is not an attack on the Lower Basin Agreement. It argues the federal plan goes further than the law allows and that the Upper Basin must share the burden.

The court filing and what comes next

As of Oct. 16, 2026, Arizona has formally intervened in the Nevada lawsuit. The case targets the U.S. Department of the Interior and the federal operating plan Burgum signed on Aug. 21, 2026.

The lawsuit aims to prevent cuts of up to 3 million acre-feet per year to Lower Basin states. It also seeks to force the federal government to enforce Upper Basin delivery obligations to Lake Mead.

No court date or ruling timeline has been announced from the sources available. Watch this space; we will update as the court sets dates.

The outcome will shape how much Colorado River water reaches your tap. It will determine how much groundwater utilities must pump as a backup. And it will set the terms for growth and farming across Maricopa, Pinal and Pima counties for years to come.

For more on how Colorado River cuts affect Valley homeowners, see our guides: Colorado River Cuts 2026: Phoenix Valley Guide and Arizona Colorado River Cuts 2027: Phoenix Impact.

Common questions

Why is Arizona joining Nevada's lawsuit over the Colorado River?

Arizona says the federal Colorado River plan violates the law of the river by forcing Lower Basin states — Arizona, Nevada and California — to absorb nearly all required water conservation while Upper Basin states like Colorado, Utah, Wyoming and New Mexico give up nothing. Arizona argues the plan could devastate the state's economy and is joining Nevada's existing lawsuit to block it.

How much water could Arizona lose under the federal Colorado River plan?

The federal plan cuts Arizona's Colorado River allocation by 760,000 acre-feet per year — nearly 250 billion gallons — for the next two years. That is roughly 27% of the state's full allocation. The lawsuit warns cuts could reach 40% after 2028.

What is the Central Arizona Project and who does it serve?

The Central Arizona Project (CAP) is a canal system that delivers Colorado River water to cities, tribes and farms across Maricopa, Pinal and Pima counties. It serves nearly 6 million people and is the primary water source for communities including Tucson.

What is the Lower Basin Agreement and does it protect Phoenix water?

The Lower Basin Agreement is a deal Arizona, California and Nevada reached in May 2026 to voluntarily conserve more than 3.2 million acre-feet of water in 2027 and 2028. Without it, the CAP's Colorado River supply would be cut by 77% over the next two years. The agreement is currently holding back the worst cuts, but it does not resolve the underlying legal dispute with the federal government.

Why aren't Colorado, Utah, Wyoming and New Mexico required to cut water?

The federal plan only mandates cuts for the Lower Basin states — Arizona, Nevada and California. The four Upper Basin states face no required reductions. Arizona's lawsuit argues this violates the law of the river, which requires Upper Basin states to deliver a minimum amount of water to Lake Mead.

Could the CAP really be cut 77%? What would that mean for Phoenix?

Yes — without the Lower Basin Agreement already in place, the CAP would face a 77% cut to its Colorado River supply over the next two years. That would force massive reliance on groundwater, likely raise water costs, and create serious uncertainty for homes, farms and businesses across Maricopa, Pinal and Pima counties.

Will my Phoenix water bill go up because of the Colorado River lawsuit?

That depends on the outcome of the lawsuit and whether deeper cuts take effect. No specific rate increases have been announced. But ADWR Director Tom Buschatzke has said the federal plan could “devastate Arizona's economy.” Greater reliance on groundwater — a more expensive alternative — could push utility costs higher over time.

Who originally filed the Nevada lawsuit and when?

The Nevada Attorney General, the Colorado River Commission of Nevada and the Southern Nevada Water Authority filed the lawsuit on Aug. 24, 2026 — three days after Interior Secretary Doug Burgum signed the final federal plan on Aug. 21, 2026. Arizona formally intervened on Oct. 16, 2026.

What is the 'law of the river' and why does Arizona say the feds are breaking it?

The law of the river is the set of compacts, court decisions and federal agreements that govern how Colorado River water is allocated and delivered. A key requirement is that Upper Basin states must deliver a minimum amount of water to Lake Mead. Arizona and Nevada argue the federal plan ignores that obligation, placing the entire conservation burden on Lower Basin states instead.