Water Resource Planning: Our Water Future

Water Resource Planning: A Quantitative Approach to Providing Water Supplies to Residents for the Next Century

The Water Resources chapter of the Utilities Integrated Master Plan (UIMP), released in draft form in 2011, has several purposes. It guides long-term planning, quantifies available water resources, and identifies infrastructure needs for water, wastewater, and reclaimed water. This chapter contains four major sections:

• Water Management, which describes historical water supply projects in Flagstaff and discusses the regulatory framework for water quality and water rights.
• Water Use and Existing Supplies, which discusses the physical and legal availability of groundwater, surface water, and reclaimed water. 
• Population Projections and Future Water Needs, which looks at possible growth scenarios and quantifies the amount of water required under each.
• Future Supply Options, which include conserving more water, adding supply wells, increasing our use of reclaimed water, and importing water. An initial economic analysis was conducted to quantify the cost per acre-foot of each supply option for financial comparison. 

Perhaps the most important result of the master planning effort is the determination that Flagstaff will face a significant supply gap over the next 80–100 years. This gap means that the City must supply an estimated 12,000 acre-feet of potable water to meet our future needs — in addition to the 10,500 Acre Feet/year we already deliver.

Master Plan Progress 

The 2011 Plan presents many options for closing the supply gap as Flagstaff grows. Among them are importing water supplies from Red Gap Ranch or the Colorado River and implementing conservation measures, which may include requiring rainwater harvesting on new developments and appliance/fixture retrofitting on existing homes to improve their efficiency. The 2011 Plan also discussed the Direct Potable Reuse (DPR) and Indirect Potable Reuse (IPR) of reclaimed water, practices that are now used in Texas, California, and elsewhere; however, it did not present costs for the various treatment technologies (the “treatment train”) required to implement this option, which were not well known at the time. As more advanced treatment plants are piloted, constructed, and become operational, we will learn more about the true costs of these technologies.

Attempts to updating this chapter have been made but a formal update has not been published. Costs for the advanced treatment of our reclaimed water supplies to implement DPR and constructed IPR strategies are still advancing and the state of Arizona has been tasked with developing regulations and rules for DPR by December 2024. IPR involves recharging treated wastewater into an aquifer or surface water body, where it can be stored and then withdrawn for later use. Any community that discharges treated wastewater to the environment already practices IPR; this requires environmental permits (AZPDES and APP) from ADEQ. However, IPR can also be permitted as a managed system by ADWR to account for recharge to the aquifer. 

This advanced treatment option raises some key questions for the Flagstaff community.

How Much Wastewater Should We Treat Using Expensive, Advanced Processes?

Scenario 1

We treat all available wastewater to the highest possible quality using advanced processes. In this case, we must decide whether existing reclaimed water customers should keep paying their current rate — or sacrifice their bottom line to pay more for water that is much cleaner than necessary for landscaping.

Scenario 2

We maintain our Class A+ reclaimed water system for existing customers and only send “excess” wastewater to the advanced treatment facility. This sounds promising, but it means there may not be enough wastewater available year-round to maintain the advanced treatment systems — unless we start treating groundwater and Upper Lake Mary water to that same high treatment standard.

How Clean Is “Clean Enough”?

Most waters — including reclaimed water — contain Contaminants of Emerging Concern (CECs) — unregulated constituents that are detected at trace levels. Over time, as laboratory technology continues to improve, we may be able to detect more contaminants at increasingly lower levels. So does this mean we continually improve our treatment technology until we can no longer detect anything? Our reclaimed water already meets Safe Drinking Water standards (for potable water). Given this, how “clean” should reclaimed water be before we can drink it? We have been proactive and sampled all of our systems for CECs to help guide decisions on how far to go with advanced treatment.

Keep in mind that even bottled water isn’t “clean.” In fact, the regulations for bottled water, enforced by the Federal Food Administration, are less stringent than those established under the Safe Drinking Water Act. Bottled water sources vary from springs — which may be high in naturally occurring minerals, such as calcium — to tap water and reverse osmosis (RO) water.