Water and Land Use in Central Arizona

More than 80% of Arizonans live in Central Arizona, (Maricopa, Pinal and Pima counties  ^1,2  ) creating an intense focus on the long-term adequacy of water supplies for the region. As people continue to move to the Sun Corridor, many wonder whether water supplies are adequate to meet demands over the long term, and to what degree it might be necessary to develop and import additional water supplies.

 Shortage on the Colorado River  complicates the subject, as do  recent determinations  that the Phoenix and Pinal Active Management Areas (AMAs) have reached regulatory limits of growth on groundwater supplies.

Although population growth is a factor in defining water demand, in Central Arizona water demand is actually more closely associated with land use choices, for example, agriculture, industrial enterprise, housing and natural open space.

Concerns about water availability prompt questions about population growth and the region's ability to support water intensive industries. Yet, many social and economic dynamics are at play. Could water needs be lessened through a cessation of subdivision growth onto native desert lands? Yes. Could water needs be ameliorated by refusing to accommodate high water-use industries? Yes. But these choices involve tradeoffs in  available housing stock , high-wage job creation and quality of life.

Decision-makers and community stakeholders ponder whether Central Arizona has enough water, but a more constructive approach may be to consider which land uses are worth the water to support them.

• The federal government exercises the power to reserve land, resulting in “reservations” for military complexes, national forests, monuments, parks and Indian Nations.
• Sovereign tribal nations have various authorities over the uses of their tribal lands.
• The State owns land that it can lease or sell. The State has the power to offer large development incentives for enterprises it wishes to lure to the region, and the State can use its taxing authorities to create both incentives and disincentives for certain types of land uses.

Cities and towns adopt zoning ordinances and as political subdivisions of the state can also use taxing authorities to create both incentives and disincentives for different types of development and land use. For example, cities typically use zoning ordinances to designate lands within their political boundaries for development or re-development as single-family residential, multifamily residential, commercial, industrial or open space. Cities can also offer financial incentives to attract desired developments. 

The tap water needs that result from land choices at the city level are generally met through the local municipal water provider. Most cities in the Sun Corridor own and operate the community water system, ensuring a connection and feedback mechanism between land use and water resource planning. In other cases, a private water company serves as the water provider, and the connection between political zoning choices and water planning may be more attenuated. Sometimes, individual landowners rely on their own wells or hauled water.

acingSpacingSpacingSpacingSpacingSpacingSpacingSpacingSpacingSpacingSpacing

The water use intensity of an area can be calculated by dividing the total amount of water delivered for all indoor and outdoor water uses by the number of developed acres.

“Urban indoor and outdoor water uses” in this context means:

• all water delivered by the local community water system
• groundwater pumping within the boundaries of the community water system but independent of the community water system  ⁵  , 
• and estimations of untreated surface water delivered for landscape irrigation where relevant.

“Developed acres” in this context means any lands that are not agricultural or undeveloped, and specifically includes lands designated for open space, because open space is an intentional land use choice.

This calculation results in the following water use per acre findings in central Arizona  ⁶  :

Because cities have different socio-economic demographics, economic goals, open-space preservation ambitions and water supplies, water use intensities will continue to differ. Yet, as the cost of water continues to rise over time, all communities will grapple with determining which land uses are worth the cost of developing additional water supplies and expanding the infrastructure necessary to deliver potable water.

1 Arizona Dept. of Water Resources, ADWR News, “How Many Homes In Arizona, On Average, Share An Acre-Foot of Water Each Year?” (April 19, 2021)  https://www.azwater.gov/news/articles/2021-19-04 . 

2 Arizona Office of Economic Opportunity, 2023 Population Estimates for Arizona’s Counties, Incorporated Places and unincorporated Balance of Counties (July, 2023).

3 Average over the municipal water providers included in the study

4 City of Phoenix, City of Glendale and Town of Gilbert, Phoenix Metropolitan Area Multi-City Water Use Study: Single-Family Residential Sector (2019)   https://www.documentcloud.org/documents/6681931-2019-Executive-Report-Phoenix-Metro-Household.html 

5 Excluding exempt wells

6 2020 data