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A 100-year water supply?

What does a guarantee certificate really mean in a time of so many cuts and changes?


Whether its groundwater or river water in danger of running dry first, the biggest potential impact from Arizona’s continuing water issues is it will stall growth.

Developers in Arizona, whose land is not connected to a designated municipal water system, must furnish certificates to show a 100 years of assured water supply, sufficient for the number of homes or types of businesses planned.

With federal restrictions recently imposed cutting the amount of Colorado River water that Arizona can use, that will likely turn up the pressure on groundwater supplies and the developments dependent on them.

Sarah Porter, director of the Kyl Center for Water Policy at Arizona State University, points out that each community in the Valley has a slightly different approach to how it gets water.

“Every city in the Valley seems to have separate challenges, and has a slightly different portfolio on where its water comes from,” Porter said. “Some have a really diversified approach.”

Much of the Valley’s water future depends, Porter said, on how the Arizona Legislature, the Central Arizona Groundwater Replenishment District and local governments decide to handle shortages and how to regulate the use of groundwater.

Assured supply

Per state rules, developers can tie into municipal systems for master-planned communities and individual subdivisions but must show a certificate of assured 100-year supplies in order to gain site plan approval.

The Arizona Department of Water Resources Assured and Adequate Water Supply programs were created to address the problem of limited groundwater supplies in the state.

There are two separate programs — one for those tying into an already-managed water zone and another for those outside those zones, often in rural or edge-of-city areas.

Both the Assured and Adequate Water Supply programs evaluate the availability of a 100-year water supply using formulas that consider current and committed demand, as well as growth projections.

These certificates must be renewed every 10 years.

The Assured Water Supply Program operates within the state’s five Active Management Areas. It is designed to sustain the state’s economic health by preserving groundwater and promoting long-term water supply planning.

AMAs are those areas where significant groundwater depletion has occurred historically and include portions of Maricopa, Pinal, Pima, Santa Cruz and Yavapai counties.

The Adequate Water Supply Program operates outside the AMAs. It ensures the water adequacy or inadequacy is disclosed in the public report provided to potential first purchasers.

Any water supply limitations must be described in promotions or advertising. However, in a mandatory adequacy jurisdiction, adequacy of water supplies must be demonstrated prior to plat approval and issuance of a public report.

To be eligible for an assured water supply based on membership in CAGRD, a subdivision owner or municipal water provider must first demonstrate sufficient groundwater is physically available to meet its proposed use for 100 years.

Under the ADWR’s assured water supply rules, groundwater is “physically available” for 100 years if it will be withdrawn from depths that do not exceed 1,000 feet below the land surface in the Phoenix and Tucson AMAs.

The maximum is 1,100 feet in the Pinal AMA, or depth to bedrock, whichever is shallower.

While at the moment, most communities within the Adequate Water Supply Program are along the edges of the developed parts of the Valley, eventually, most of that development will be one large continuous block with the rest of the Valley.

Issues with relying on groundwater

Porter and senior ASU research fellow Kathleen Ferris are the lead authors of “The Elusive Concept of an Assured Water Supply: The Role of CAGRD and Replenishment.” The late-2019 report offers many criticisms of the current permission and speculation system of allowing dependence on groundwater and offers some solutions.

“For nearly 40 years in its most urban areas, Arizona has prohibited the sale of subdivision lots that lack a 100-year assured water supply,” the report says. “Originally, an assured water supply meant primarily surface water, which nature renews annually.”

However, in 1993, the legislature changed course and created a new path to show an assured water supply using groundwater — which the Kyl Institute calls a nonrenewable resource — with the promise that groundwater would be replenished with surface water acquired later by CAGRD.

Restrictions on Colorado River water distribution are just one example of how increasing difficult it will be to obtain effluent supplies to replenish groundwater pumped up from aquifer pockets.

However, the pumping of wells itself creates several new problems, the report says.

“Studies show that the quality of groundwater at such great depths can be seriously compromised as natural and man-made pollutants concentrate in the water that remains,” the report says. “Moreover, as the underground water table declines, groundwater aquifers collapse and lose their capacity to store water, making their replenishment impossible.”

The report also says CAGRD is not required to replenish water where groundwater is pumped for its members, so the fix is not necessarily at the site where the pumping took place.

This creates local geological problems, the report says. The cost to everyone, according to Spencer Kamps of the Central Arizona Homebuilders Association, including eventual home buyers, is affected by the price of water.

Some homebuilders are spending millions to purchase 10 years worth of water, he said.

“In the cities with designations, I don’t know how the lack of Colorado River water will affect home prices. We’re just not sure yet, but it will be indirect,” Kamps said. “In the non-designated areas, like Buckeye or parts of Pinal County, yes, the cost of purchasing water is passed along. But the cost of buying water is just one of many, many factors in how a finished home is priced.”

Doing things differently

The Southwestern states must find different ways to find water. In addition to Gov. Doug Ducey signing a bill providing $1.2 billion for what he calls the largest desalination project in history, he called for everyone to think about solutions in an open-minded, imaginative way.

In an Oct. 17 news release, the Central Arizona Project said it’s committed to helping CAGRD fulfill its statutory replenishment requirements and aggressively pursuing both new surface water rights and new ideas for how to get water to central Arizonans.

“CAGRD is also focused on pursuing new water supplies available in times of shortage,” CAP said in the release. “For many years, CAGRD has been preparing for having less CAP water ... CAGRD will continue to forecast and monitor the potential shortage impacts to existing water supplies and finances. The focus will be on the wise use of resources to meet replenishment obligations at the lowest cost for our members and to continually acquire new supplies for future obligations.”

The Elusive Concept report calls for these changes to how groundwater is allocated prior to new construction:

• CAGRD and ADWR should be required to more rigorously review how much water for replenishment is realistically available.

• ADWR should decrease the depth from which groundwater may be withdrawn for purposes of an assured water supply to prevent the damage caused by draining aquifers. Thus will also protect the quality and availability of groundwater for the future and will ensure against “the very real possibility that groundwater in some areas may run out.”

• CAGRD should be required to replenish water in the same locations where groundwater is pumped for its members. It should be required to have the necessary facilities for such replenishment in place before new members in these locations can enroll in a program, or as a strict prerequisite for the sale of lots in these areas. 

• CAGRD should be authorized to deny membership if it runs into problems acquiring water for replenishment or in locating and constructing replenishment facilities.

• A comprehensive review of CAGRD’s financing mechanisms should be completed. This would help avoid a financial catastrophe and protect homeowners on CAGRD member lands from skyrocketing costs.

Kamps points out that in the older Valley cities, replenishment at the site of withdrawal is difficult because built-out cities aren’t always suited to have water seep into the aquifer at the same spot.

He said the  Elusive Concept's report recommendation that ADWR deny membership is unnecessary, as there are already mechanisms in place to  either deny or simply not issue new certificates and/or designations.

Cities that are still growing and don’t have designations, such as Buckeye, can plan and allow for replenishment at the same site.

He also points out effluent and replenishment are inventions brought about by home development and are more effective water uses than agriculture.

“The reasons the Valley, with almost 6 million people, uses about the same amount of water as it did in 1957 are, one, conservation and, two, building for-sale housing where higher-use properties were, or could have gone,” he said. “We’ve helped retire some (agriculture) rights. Only one type of land use — home-building — slowed the rate at which water was being consumed before.”

He said there has long been frustration among homebuilders that residential developers must prove a 100-year supply, but industrial and commercial developers in Arizona aren't held to the same standard.

Kamps said he won’t discuss which specific changes he sees being discussed in the 2023 Arizona legislative session.

However, with desalination years away in development, he’s certain the legislature will end up discussing water in 2023, in some manner.

“We need more water solutions now,” he said.