Effluent Recharge Policy Platform

Scope: The Upper Santa Cruz Sub-Basin of the Tucson Active Management Area (i.e. the Tucson Basin in Pima County).

I. Background

            Reclaimed water, or effluent, is the sole increasing water source in Arizona.[1] Effluent generally increases along with population growth, though urban water conservation reduces effluent production in proportion to implementation of indoor water consumption efficiencies.

            Title 45, Chapter 3.1 of the Arizona Revised Statutes governs the credit system for storing water, including effluent, in underground aquifers. Permit holders earn long-term storage credits when they store water in a way that complies with legal requirements; those credits can then be used to later recover stored groundwater or to provide an assured water supply for new development.[2] The current credit system awards full 100% credits to water stored at a “constructed” underground storage facility (USF) and 50% credits to water stored at a “managed” USF.[3]

            Though there is no statutory definition for “constructed,” such facilities are typically basins or pits located outside of natural waterways. Stream and riverbeds, such as the Santa Cruz River, qualify as “managed” facilities. Thus, a permit holder receives double the credits for the same amount of stored water when the water is recharged through a “constructed” facility than a “managed” facility. There are multiple locations on the Santa Cruz that could qualify for the "constructed" recharge credit rate due to constructed infiltration features in the riverbed, that are currently receiving only the "managed" rate.

            The 50% “cut to the aquifer” for managed recharge was originally designed to encourage effluent use and improve safe yield (balance groundwater pumping with natural recharge). However, the Tucson region, in its efforts to increase sustainability, has achieved these goals independently of the credit-based incentive. Additionally, these cuts to the aquifer are unlikely to continue as economic incentives cause effluent owners to divert water from the river to constructed underground or groundwater savings facilities.

            Off channel recharge can cause new problems for rivers and aquifers that impede their recovery and maintenance. As ADWR has found in its Water Accounting Areas and Enhanced Aquifer Management efforts, recharging groundwater downstream of pumping locations creates imbalance and vulnerability in riparian areas. Alternative solutions that benefit rivers and aquifers while addressing sustainability goals are available: for example, Pima County’s proposal to deliver effluent to Vail Water to help restore flows to Cienega Creek, at the upstream end of the Upper Santa Cruz watershed.

            As Arizona’s sole increasing water source, effluent presents a water supply opportunity. And as a high-quality source, one of its potential uses is the restoration of degraded riparian habitat. Up to 90% of Arizona’s riparian areas have been degraded or lost over the last century as a result of human impact and development.[4] Nationally, at least 50% of riparian areas have been altered or converted to other land uses. Riparian areas are rare and disproportionately important in the Southwest, covering less than 2% of land area and providing a lifeline to the majority of migrating and resident wildlife.[5] Projects with multiple goals, such as restoration and storage via recharge, are possible and should be encouraged.       

            Today, the majority of the surface flow in the Santa Cruz River is effluent,[6] and the river’s only perennial flows occur in “effluent-dominated” stretches downstream of wastewater treatment plants.[7] Approximately 50,000 acre-feet of annual effluent discharge in the Lower Santa Cruz[8] create thriving riparian habitats that support over 200 bird species and, in some areas, non-native fish.[9] Although human populations have been increasing, the amount of effluent released into the Santa Cruz has been declining since at least 2004, due in part to greater water conservation, but also to increased diversions.[10] More water is at risk of being diverted off-channel due to the economic, credit-based incentive to remove water from the river for the purpose of earning more long-term storage credits.[11] As Colorado River water supplies decrease and human demands for potable water, including effluent, increase,[12] incentives to divert effluent off-channel threaten riparian habitats that depend on effluent-dominated portions of the Santa Cruz for their continued existence.

II. Analysis

            Maintaining surface flows in the Santa Cruz is critical to restoring lost riparian habitat and Southern Arizona’s heritage of flowing desert rivers. Most historically perennial stretches of the Santa Cruz in the Tucson area have dried up due to excessive groundwater pumping, and although current effluent-dominated areas were not historically stretches of perennial flow, today they support a range of riparian habitat critical for human and environmental health.

            A flowing river benefits adjacent and nearby communities. Cooler temperatures, higher property values, erosion and flood control, and more opportunities for recreation, tourism, and alternative transportation are just a few of the benefits a flowing Santa Cruz provides in the Santa Cruz Active Management Area.[13] A recent study found that the riparian ecosystem of Tucson’s Sabino Creek provides at least $1.4 million in ecosystem services each year[14], and a growing body of research shows that well managed “blue spaces” (visible water in urban areas) support mental and physical health.[15]

            Of particular concern in southern Arizona is the “urban heat island” effect that occurs in urban areas where temperatures are higher due to a higher density of impervious surfaces and lack of trees. According to the Environmental Protection Agency, urban heat islands “affect human health by contributing to general discomfort, respiratory difficulties, heat cramps and exhaustion, non-fatal heat stroke, and heat mortality... Sensitive populations, such as children, older adults, and those with existing health conditions are at particular risk from these events.”[16] Moreover, changes in climate are expected to result in increased temperatures, which, left unchecked, will cause more incidents of heat-related illness. A healthy, flowing river and the vegetation it supports will help mitigate and prevent the adverse public health effects of urban heat islands.[17]

            Flowing rivers also offer direct economic benefits to urban areas. Tempe, AZ, Sacramento, CA, Portland, OR, and San Antonio, TX are just a few examples of cities where a downtown “river walk” attracts and supports tourism and economic activity. Tucson Water recently announced a similar proposal for downtown Tucson, called Agua Dulce: The Santa Cruz River Heritage Project.[18] 

            The many benefits of increasing in-channel effluent deployment and recharge include: restoring historically perennial sites and shallow groundwater, improving wildlife habitat and connectivity, enhancing public accessibility and economic development, managing floodplain riparian vegetation, increasing recycled water use and Conservation Effluent Pool deployment, pursuing economic incentives and recharge credits, and balancing withdrawal and recharge efforts through upstream aquifer replenishment, thereby creating a secure future for water in the Santa Cruz.

            As Arizona’s water resource supply-demand gap grows, the value of and demand for effluent will almost certainly increase. Time is of the essence in establishing policies that protect and promote effluent-dominated portions of the Santa Cruz.

III. Recommendations

  • CWC recommends continued and increased cooperation among stakeholders to maintain flows in effluent-dominated portions of the Santa Cruz River. CWC recommends that stakeholders seek water management solutions that serve multiple functions and meet both economic and environmental needs.


  • The Santa Cruz River has great value as a riparian corridor and as a cost-effective groundwater recharge facility. CWC recommends a collaborative effort to facilitate a long-term storage credit system to recognize and enhance both of these functions.


  • CWC recommends development of an integrated river restoration and management plan for the Santa Cruz River. Such a plan would address the challenges to implementing in-channel recharge in the Santa Cruz, including the lack of a statutory definition for “constructed” recharge, a complicated land ownership scheme, and a multitude of regulatory jurisdictions. CWC recognizes that “river engineering” presents significant concerns with respect to hydro-modification, and is prepared to assist in addressing these challenges.


  • CWC recommends implementing constructed recharge projects in the Santa Cruz River. ADWR has indicated that even though the term “constructed” is not statutorily defined, it will interpret the term broadly and provide 100% recharge credits for constructed in-channel recharge. Ongoing construction projects at the Ina Road and Sunset Road bridges provide an opportunity to dovetail ongoing construction with constructed in-channel recharge facilities that will yield 100% recharge credits while simultaneously preserving surface flows.


  • CWC recommends the use of in-channel constructed recharge facilities because these facilities serve multiple functions, including flood control, reduced maintenance costs, erosion control, and preservation of pollinator and migratory bird habitat.


  • CWC recognizes the challenges involved in 1) meeting federal obligations to Indian tribes under SAWRSA and 2) devising a general management plan for the Santa Cruz River that will include maintenance of in-channel constructed facilities. CWC believes that solutions are available to meet the needs of economic development, agriculture, and Native nations.


  • CWC recommends linking conserved water, including effluent, to the restoration of natural ecosystems. As water conservation efforts increase, conserved water should be used to restore Arizona’s lost rivers.


  • CWC recommends broader and stronger state-level legal protections for in-channel environmental flows, including effluent-dominated sections of the Santa Cruz River that support rare riparian habitat.


[1] Arizona Department of Water Resources, Securing Arizona’s Water Future http://www.azwater.gov/AzDWR/PublicInformationOfficer/documents/supplyd…

[2] A.R.S. § 45-855.01, Effect of long-term storage credits on assured water supply and adequate water supply

[3] Arizona Department of Water Resources, Recharge Credits and Accounting, available at http://www.azwater.gov/azdwr/WaterManagement/Recharge/RechargeCreditsan…

[4] Human Alterations to Riparian Areas by George Zaimes, available at http://cals.arizona.edu/extension/riparian/pub/UARA_07-17-07_chapter7.p…; Arizona Riparian Council, at https://azriparian.org/.

[5] Arizona Riparian Council; George Zaimes, Defining Arizona's Riparian Areas and Their Importance to the Landscape, University of Arizona College of Agriculture and Life Sciences, https://cals.arizona.edu/extension/riparian/pub/UARA_07-17-07_chapter1….

[6] Jacob Prietto, Stakeholder Incentives for Effluent Utilization in the Tucson Metropolitan Region and Recharge in the Santa Cruz River, available at http://www.cap-az.com/documents/education/2013-Prietto.pdf at p. 12.

[7] Santa Cruz could flow again through downtown Tucson, by Tony Davis, Arizona Daily Star, November 8, 2016 http://tucson.com/news/science/environment/article_1aac5f08-445f-544a-b…

[8] Prietto at p. 8.

[9] The Sonoran Institute, A Living River report, available at https://sonoraninstitute.org/2016/lower-santa-cruz-river-study-results/


[11] Stakeholder Incentives, http://www.cap-az.com/documents/education/2013-Prietto.pdf, p. 9; Tony Davis, River Recharge Efforts Under a Disadvantage in State Law, Arizona Daily Star, available at http://tucson.com/news/science/environment/river-recharge-efforts-under-a-disadvantage-in-state-law/article_766c40b1-0529-52e4-b526-55dc24208330.html; As Arizona’s Effluent Becomes More Valuable, Some Worry Rivers Could Lose Out, Will Stone, KJZZ, July 2015, available at http://kjzz.org/content/332470/arizonas-effluent-becomes-more-valuable-some-worry-rivers-could-lose-out

[12] See Closing the Water Demand-Supply Gap in Arizona in the 2015 issue of the Arroyo, published by the Water Resources Research Center at the University of Arizona, available at https://wrrc.arizona.edu/sites/wrrc.arizona.edu/files/Arroyo-7-24-2015…

[13] See Ecosystem Services of Bi-national Effluent in the Upper Santa Cruz River Watershed, Laura M. Norman, PhD for USGS, June 2012, available at http://www.azmc.org/wp-content/uploads/2012/06/7-Ecosystem-Services-of-Binational-Effluent-in-Santa-Cruz-River-Watershed_June2012.pdf

[14] Earth Economics, The Value of Ecosystem Services in Lower Sabino Creek https://watershedmg.org/sites/default/files/documents/sabino-creek-economic-valuation-report-2016.pdf

[15] Tim Smedley, What Impact Do Seas, Lakes, and Rivers Have on People’s Health?, The Guardian, March 2013, available at https://www.theguardian.com/sustainable-business/impact-sea-lakes-rivers-peoples-health

[16] Heat Island Impacts, Compromised Human Health and Comfort, The Environmental Protection Agency (EPA) available at https://www.epa.gov/heat-islands/heat-island-impacts#health

[17] Heat Island Cooling Strategies, EPA, available at https://www.epa.gov/heat-islands/heat-island-cooling-strategies

[18] Santa Cruz could flow again through downtown Tucson by Tony Davis, November 7, 2016, The Arizona Daily Star, available at http://tucson.com/news/science/environment/article_1aac5f08-445f-544a-b…