What Arizona water law means for a yard

Arizona’s water law is often described as though it were a set of rules about gardens. It is not. The state’s framework is built around basins, subdivisions and providers: big units, long time horizons, paperwork handled by developers and water companies. The rules that actually shape what a household can do with a yard come from somewhere else entirely, and finding them is the practical part of this subject.

This page sets out the framework as the statute and the agencies describe it. It is not legal advice, and it deliberately does not try to answer a question about a specific address.

What the state law actually regulates

The framework begins with the Groundwater Management Act of 1980, which is codified as the Groundwater Code in Title 45, Chapter 2 of the Arizona Revised Statutes. The code states its own purpose in § 45-401, and the two findings in that section explain most of what follows: that in numerous basins pumping exceeds what can be sustained, and that groundwater use should therefore be allocated to its most beneficial and economically effective purposes.

The code is administered by the Arizona Department of Water Resources, the state agency responsible for groundwater regulation, the designation of the management areas, and the water-supply determinations described below.

Within the state’s most depleted basins, the code created Active Management Areas. The Phoenix AMA is one of the first five, alongside Pinal, Prescott, Tucson and Santa Cruz, and it covers the built-up Valley. Each area has a statutory management goal. For the Phoenix AMA, § 45-562 sets the goal as safe-yield (a long-term balance between what is pumped and what returns to the aquifer) with 1 January 2025 as the date the statute names. Progress against that goal is tracked through a sequence of management plans, each more demanding than the last, covering agricultural, municipal and industrial users.

None of that reaches into a residential garden. It governs who may pump, how much, and for what.

The Phoenix AMA and the assured supply rule

The part of the code with the widest practical reach is the assured water supply requirement, and it applies to land rather than to households.

Under A.R.S. § 45-576, a person proposing to offer subdivided land for sale or lease inside an active management area must generally obtain a certificate of assured water supply from the director of ADWR before the plat is approved. The requirement is satisfied either by that certificate or by a written commitment of water service from a city, town or private water company that ADWR has designated as having an assured water supply. A city may not approve a subdivision plat unless one of those two showings exists.

The definition does the heavy lifting. An assured supply means sufficient groundwater, surface water or effluent, of adequate quality, continually available for at least one hundred years, with the projected groundwater use consistent with the area’s management plan and goal, and financial capability demonstrated to build whatever is needed to deliver it. For some applicants inside a groundwater replenishment district, the statute measures the proposal against a depth to water of 1,000 feet or the bottom of the aquifer, whichever is less.

Two things about this are worth holding on to. The first is that the 100-year standard falls on a subdivision or on a provider, not on an individual. The second is that it is a test of a paper plan, not a tap restriction. A household inside a designated city’s service area never fills in this form; the city already did.

Where the water comes from

Arizona’s Colorado River water arrives through the Central Arizona Project, authorised by the 1968 Colorado River Basin Project Act and operated since 1971 by the Central Arizona Water Conservation District. It is a 336-mile aqueduct from Lake Havasu, lifting water about 3,000 feet through 15 pumping plants to reach central and southern Arizona. In-state rivers (the Salt and the Verde among them) supply part of the Valley’s surface water, and the rest comes from groundwater beneath the basins.

The pressure on all of it is easiest to see at the scale of the whole river.

That gap is the reason a shortage can be declared on a river that still has water in it. Arizona’s share of a shrinking supply is smaller than its share of the paper allocation, and the reductions land on the users whose priority dates are latest, which, in practice, has meant agricultural districts and the state’s water-banking arrangements before it has meant a city tap. None of that changes what a household may water on a Tuesday, but it is the backdrop to every conversation about growth in the Valley.

Why none of that is a rule about your yard

Here is the sentence that matters most on this page: no part of the Groundwater Code sets a watering day, a watering time, or a list of permitted plants for an existing household garden.

The code operates upstream of the tap. It decides who may pump groundwater and where, whether a new subdivision may be platted, and whether a city or water company may be designated as having a supply. A garden hose is well downstream of all three. If you go looking in Title 45 for something that tells you when to run your drip lines, you will not find it.

It is also worth being clear about what the state law does not do, because that is where most of the confusion lives. It does not ration outdoor water across the state during a drought. It does not require a permit for a landscape. It does not know which plants are in your yard.

What actually applies to your yard

Three things do, and they vary more than people expect.

The first is the water provider. Whether that is a city water department, a private water company, or a community system, the provider publishes the rules that apply to its customers: any watering-day schedule, any time-of-day restriction, and any drought stage in force. Two houses on the same street in different service areas can be under different schedules.

The second is the city or county. Landscape conditions can attach to land at the point of development: through a subdivision’s own plat, through a municipality’s development standards, or through an ordinance applying to new construction. Those conditions can travel with the land.

The third is the lot itself. The plat, the subdivision’s recorded conditions and the provider’s service area are specific to an address. The same species of tree can be entirely fine in one Valley neighbourhood and subject to a condition elsewhere, and the reason is almost never the plant.

What this page will not tell you

It will not tell you what applies to your address, and it cannot. Water rules vary by provider, by city and by lot, and a page that tried to generalise across them would be wrong somewhere in the Valley by definition.

It is also not legal advice, and it is not a substitute for the current version of a document. The framework above is stable; the detail underneath it moves faster. ADWR’s rules for the Phoenix AMA have been revised more than once since the groundwater model was updated in 2023, and those changes have been the subject of litigation, so a summary written a year ago may already describe a rule that has been replaced.

If you want the answer for your own address, go to the two places that hold it: your water provider’s current published rules, and your city’s development or water conservation office. For the state-level picture, ADWR is the agency that administers the code, and it publishes the current status of the assured water supply programme itself.

What this means for planning a yard

The practical conclusion is almost anticlimactic. Arizona’s water law shapes whether a new neighbourhood can be built and whether a city can promise water for it. It does not tell you how to plant the yard you already have. What it does tell you, indirectly, is the direction of travel: a state that measures supply in hundred-year blocks is a state where outdoor water is the part of the bill with room in it.

That is the case for grouping plants by how much water they actually need, which is what the Hydrozone Yard Planner is built to do, and for choosing species before choosing a layout, which is what the Desert Plant Picker is for. Neither is a legal requirement. Both are the cheapest way to keep a yard out of the argument. For the bigger picture on outdoor water, Desert lawns: water and what they ask for is the companion piece, and Hydrozoning a desert yard takes the grouping idea further.