Flagstaff Reuse 101 and Other Facts

Definitions of important terms:

  • Potable water: Drinking water that meets or exceeds state and federal drinking water standards for human consumption
  • Non-potable water: not for human consumption
  • Influent: The untreated wastewater or raw sewage coming into a wastewater treatment plant 
  • Effluent: Liquid that flows out of something, in wastewater the final output flow from a wastewater treatment plant
  • 1 Acre-Foot = A way to reference large volumes of water. One acre-foot equals about 325,851 gallons, or the equivalent of a football field one foot deep of water. Flagstaff reclaimed customers use about 2,000 acre-feet in a year while potable customers use about 8,000 acre-feet of water in a year.
  • C-Aquifer: The C aquifer underlies the Little Colorado River Basin and parts of the Verde and Salt River Basins and is named for the primary water-bearing rock unit of the aquifer, the Coconino Sandstone. The areal extent of this aquifer is more than 27,000 square miles
  • Compounds of Emerging Concern (CECs) are synthetic chemicals that are presently unregulated but for which there is scientific concern that they may be hazardous to the health of people, other species, or the environment. They are not presently regulated because there is insufficient testing or knowledge to set science-based safe limits or there has been a decision not to regulate. They include selected pharmaceuticals, personal care products, herbicides, pesticides, industrial cleaning agents, and fire retardants.  When found in public water supplies, they often occur in extremely low concentrations - nanograms per liter, or, parts per trillion (ppt). Despite low concentrations, some of these chemicals are known or suspected to pose risks to human health and aquatic organisms.
  • Parts per (million, billion, trillion) are used to express small concentrations of contaminants in water. Over the past 50 years, scientist have expanded the ability to detect smaller and smaller amounts of substances in water. The following units will be used to indicate the amount of a of contaminant in reclaimed water:
    • ppm: parts per million or milligram per Liter (mg/L). This is roughly the equivalent of 7 drops of ink in 1 bath tub of water 
    • ppb: parts per billion or microgram per Liter (μ/L) This is roughly the equivalent of 1 drop of impurity in 500 barrels of water              (1 barrel = 42 gallons)
    • ppt: parts per trillion or nanogram per Liter (n/L) This is roughly the equivalent of 1 drop of impurity in 500,000 barrels of water


What is reclaimed water and how is it produced? 

  • Reclaimed water is collected wastewater (influent) that is treated for the purpose for reusing or recycling. It is produced through a series of physical, biological, and chemical treatment processes, which determine the effluent class and its permitted use. Water Services produces Class A+ reclaimed water for non-potable use as permitted by the Arizona Department of Environmental Quality for the following uses: irrigation of food crops, recreational impoundments, residential landscape irrigation, school ground landscape irrigation, open access landscape irrigation, toilet and urinal flushing, fire protection systems, spray irrigation of an orchard or vineyard, commercial closed loop air conditioning systems, vehicle and equipment washing, and snowmaking.
  • Both of Flagstaff’s wastewater plants are water reclamation plants. The Wildcat Hill Water Reclamation Plant and Rio De Flag Water Reclamation Plants produce Class A+ reclaimed water using the following processes: 
    1. Primary Treatment/Physical Process: Influent flows through a bar screen and grit removal system to remove large debris and inorganic solids. The water then flows to the primary clarifier where heavier organic solids settle to the bottom of the tank while lighter solids float to the surface, and both are removed. 
    2. Secondary Treatment/ Biological Process: The water then undergoes biological nitrogen removal, converting remaining organic matter in settleable solids, which are removed by the secondary clarifier. 
    3. Tertiary Treatment/Physical and Chemical Process: Finally, the water enters the sand filtration areas, which remove any remaining particulate matter and is then disinfected with either chlorine or UV rays to neutralize any remaining pathogens. 
  • Advanced Treatment includes additional treatment processing that removes trace contaminants. Advanced treatment options include: membrane filtration, membrane desalination, ozone, and advanced oxidation. Advanced treated water exceeds the standards of Class A+ water. 
  • Advanced Purified Water has been treated through multiple stages of advanced treatment processes and has been verified through monitoring to be safe for augmenting water supplies. Purified water is safe for potable use by way of blending with surface water and groundwater supplies, or being added directly into the water distribution system. 


How does Flagstaff currently use reclaimed water?

  • Reclaimed water accounts for about 20% of total water use in Flagstaff.
  • The City operates two water reclamation plants that have the capacity to produce a combined 10 million gallons of Class A+ water per day for non-potable reuse. Once treated, this water is either transported to users in a separate distribution system (“purple pipe”) for reclaimed uses like landscape irrigation, dust control and for flushing toilets, or the reclaimed water not used is discharged to the Rio de Flag. Only one-third of the reclaimed water produced each year is committed to current customers. 
  • The remaining two-thirds of uncommitted reclaimed water that is discharged into the Rio de Flag at the I-40 wetlands or through Picture Canyon has developed a riparian ecosystem at both locations. Some reclaimed water also infiltrates into the ground, is naturally filtered through an initial unsaturated layer called the Vadose Zone, and mixes with groundwater supplies in the C-Aquifer. Only some of the portion of reclaimed water released to from the Rio de Flag Water Reclamation Plant recharges the C aquifer above gradient of several of the City’s groundwater production wells, referred to as  recharge and recovery or De Facto reuse.  


How could reclaimed water help to meet Flagstaff’s future water needs?

  • Flagstaff operates under a water supply planning permit through the Arizona Department of Water Resources, termed a Designation of Adequate Water Supply. The Permit signifies that the City has demonstrated physical supply availability for 100 years, legal rights to water, water infrastructure, as well as financial and water treatment capabilities, to meet build-out water demands for the voter-approved Flagstaff Regional Plan 2030. Flagstaff currently meets the requirements of the designation with surface water,  groundwater, and reclaimed water supplies. 
  • Population and water use projections indicate that Flagstaff will need to secure an additional 7,700 to 16,500 acre-feet per year to maintain its Designation of Adequate Water Supply. The City is exploring several future water supply options to meet projected needs, including expanded use of its reclaimed water. Increased reclaimed water development could help to offset even more potable water used for non-potable purposes, or be add directly to the potable water supply. Each option contributes towards water management sustainability, depending on the management approaches recommended by the Community Stakeholder Committee on Reclaimed Water (CSCRW. 
  • The Reclaimed Water Master Plan will include a more detailed analysis of the management alternatives recommended by the CSCRW. The Master Plan will detail those options for reclaimed water as alternatives to project, such as Red Gap Ranch, into the City’s Water Resources Master Plan. 


Which reclaimed water options are being considered for Flagstaff in the future?

Water Services contracted with Carollo Engineers in 2017 to explore the various options the City can consider for expanding use of reclaimed water in Flagstaff. That report is available here . In summary, the report explored a number of options for reclaimed water, with the exception of “additional reclaimed water infrastructure, which will be detailed in a similar amount of detail during Workshop 2 of the CSCRW.

  • Option 1. Current and future opportunities for expanding the reclaimed distribution system – referred to as direct reuse
  • Option 2a. Aquifer recharge through a managed recharge permit (streambed recharge) – a form of indirect potable reuse with advanced treatment beyond Class A+
  • Option 2b. Aquifer recharge through a managed recharge permit (streambed recharge) – a form of indirect potable reuse without advanced treatment beyond Class A+
  • Option 3a. Aquifer recharge through a constructed recharge permit (groundwater recharge wells) – a form of indirect potable reuse with advanced treatment beyond Class A+
  • Option 3b. Aquifer recharge through a constructed recharge permit (groundwater recharge wells) – a form of indirect potable reuse without advanced treatment beyond Class A+
  • Option 4. Pipeline to Upper Lake Mary – a form of indirect potable reuse through surface water augmentation with advanced treatment
  • Option 5. Drinking water – direct potable reuse with advanced treatment and purification


What are the next steps?

  • The next steps start with you! The Community Stakeholder Committee on Reclaimed Water will be vital in narrowing down which reclaimed water options should be incorporated into the Water Resources Master Plan. 
  • The feedback provided at these meetings will be used in the development of the Reclaimed Water Master Plan. The Committee will provide a formal recommendation on their top ranked projects.

A profile on Arizona water reuse from the WateReuse Association can be read here.