Backflow Prevention & Pretreatment

Water Services is dedicated to protecting our City water and sewer systems from harmful or unwanted substances, and ensuring that everything flows in the right direction. The following programs protect our systems and our community from the risks of contamination.

Archived Notice of Code Changes:

Part 2: Cross-Connection and Local Limits for SIUs

Backflow Prevention

The water distribution system in Flagstaff is designed to keep water flowing to you, the customer. However, hydraulics can sometimes deviate from "normal" conditions, reversing flow and causing contaminated water from homes or businesses to enter the distribution system, known as backflow. The Cross Connection Control Program avoids potential occurrences of backflow contamination through installation of backflow valve assemblies in locations where conditions could exist that would allow contaminated water to enter the distribution system. Visit our Backflow Prevention and FAQs pages to learn more. 

Pretreatment Program

The Industrial Pretreatment Program provides monitoring, permitting and reporting of industrial and commercial wastewater discharges into the City of Flagstaff sewer system. Industrial byproducts can interfere with the processes at the City's reclamation plants and potentially contaminate the Rio de Flag. The Pretreatment Program assures compliance with Local, State and Federal mandated pretreatment regulations, which reduces the amount of pollutants discharged into the City's collection and treatment facilities.

Per ADEQ and EPA requirements, the City of Flagstaff prepares an annual report describing the activities of the Industrial Pretreatment program for the previous calendar year. The 2022 Industrial Pretreatment Annual Report (PDF) is now available. If you have any questions about the report or additional inquiries, please contact Industrial Pretreatment at  

Enforcement Response Plan

The Enforcement Response Plan (PDF) (ERP) contains detailed procedures for commercial, industrial and construction users on the monitoring of cross-connection control, stormwater, and industrial pretreatment activities, as well as Water Services' levels of response to instances of noncompliance in these three programs. Criteria such as significance, severity, duration of a violation, and the good faith of the operator are considered when determining enforcement action.