Last Updated 07/20/2026
The City of Phoenix has enacted a Stormwater Ordinance in order to establish minimum stormwater management requirements and controls to protect and safeguard the general health, safety, and welfare of the public residing in watersheds within this jurisdiction. The City of Phoenix is the permitting authority for all land disturbing activities and requires the land owner to maintain all on-site stormwater control facilities and all open space areas (e.g. parks or “green” areas) required by the approved stormwater control plan. The City of Phoenix will only provide construction permits to projects that establish a plan to manage stormwater runoff occurring during the construction process. The City of Phoenix, under the NPDES program, also has the authority to inspect properties for noncompliance and can issue a notice of violation (NOV) for any deficiency or infraction onsite. Property owners are responsible for the maintenance of any stormwater facilities or practices located on the property. The City of Phoenix has the authority to inspect stormwater facilities and practices in order to ascertain that they are properly maintained and functioning.
Maricopa County Stormwater Management Plan
2.0 Introduction
This Stormwater Management Plan (SWMP) was created in response to the Arizona Pollutant Discharge Elimination System (AZPDES) General Permit AZG2016-002. The SWMP is the principal means in which Maricopa County (County) has recorded programs and policies to demonstrate full permit compliance. Under the general permit, the County must implement actions and activities that demonstrate compliance with permit requirements. These actions are called Minimum Control Measures (MCMs) and include:
- Public Education and Outreach
- Public Involvement and Participation
- Illicit Discharge Detection and Elimination
- Construction Site Runoff Control
- Post-Construction Runoff Control
- Pollution Prevention & Good Housekeeping for Municipal Operations
The County has developed Best Managing Practices (BMPs) for each MCM. Each MCM and their corresponding BMPs are outlined and detailed in Section 6.0 of this SWMP.
6.5 Post Construction Stormwater Management
Existing Maricopa County regulations require that developments receive and retain stormwater volume generated by a two-hour, 100-year precipitation event. Retention basins are required to be located not less than 25 feet from septic systems. Runoff that has been retained onsite must be disposed of within 36 hours by percolation, dry wells, or drainage into an approved drainage way, not to exceed pre-development flows. Disposal of stormwater is considered essential for vector control. The drainage regulations also contain language designed to ensure stability and prevent erosion in hillside developments. An inventory of all post construction stormwater structures is maintained. This inventory fluctuates at properties and land are annexed over time.
City of Phoenix Stormwater Policies and Standards
(Sec. 3.9)
3.9 Maintenance
It is essential that maintenance be considered during the planning, design and construction of drainage facilities. Maintenance is provided so that the facilities can function as they were originally designed and constructed, and so that the service life of the facility is maximized. Common maintenance problems associated with drainage facilities include growth of unwanted vegetation, debris accumulation, sedimentation, erosion, scour, soil piping, soil settlement and structural damage. Culverts and bridges are to be designed to avoid impacts to existing sediment transport conditions. Provision for permanent drainage facility accessibility, including access for maintenance equipment into channels and culverts, is necessary for regularly scheduled maintenance activities.
3.9.5 Private Maintenance
All drainage facilities owned and/or operated by private entities, including Homeowner’s Associations, shall be properly maintained to promote performance of the drainage facilities consistent with the original design intent.
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Frequently Asked Questions
How much stormwater do I need to retain on-site under Maricopa County's drainage regulations?
Enough to capture a two-hour, 100-year precipitation event. That’s a demanding design standard, and once retained, that runoff has to be disposed of within 36 hours through percolation, dry wells, or drainage into an approved drainageway, without exceeding pre-development flow rates.
Is there a setback requirement for retention basins in Maricopa County?
Yes. Retention basins have to sit at least 25 feet from any septic system. That’s a design constraint worth confirming early in site planning, particularly for properties where septic infrastructure and retention capacity are competing for the same portion of the lot.
Does Maricopa County inspect post-construction stormwater controls after they're built?
Yes, through an ongoing program that combines education and inspection. The county’s post-construction BMP inspection program confirms that structural and non-structural controls were built to the approved standard and checks that they continue to be maintained afterward, rather than treating the initial approval as the end of oversight.
Who is responsible for maintaining stormwater drainage facilities on private property in Phoenix?
The property owner or operating entity, including homeowner’s associations. The city’s stormwater policies specifically require private entities to properly maintain their drainage systems so they perform as designed, and that responsibility carries extra weight heading into monsoon season, when systems face their heaviest test.
What kinds of maintenance problems does Phoenix expect property owners to watch for?
Unwanted vegetation growth, debris accumulation, sedimentation, erosion, scour, soil piping, soil settlement, and structural damage are all called out specifically in the city’s drainage standards as common issues that undermine a facility’s original design intent. Left unaddressed, any of these can shorten a system’s service life well before the end of its expected design lifespan.
Does Phoenix require drainage facilities to stay accessible for maintenance equipment?
Yes. The city’s design standards require permanent accessibility into channels and culverts specifically so maintenance equipment can perform regularly scheduled upkeep. That’s a design consideration worth flagging early, since retrofitting access into an existing system is far more disruptive than building it in from the start.
Does Maricopa County track which properties have post-construction stormwater structures?
Yes, through a maintained inventory that adjusts as properties and land are annexed over time. That means a change in a property’s jurisdictional status can affect how its stormwater infrastructure is tracked, even without any physical change to the system itself.
How can AQUALIS help my property stay compliant in Phoenix or Maricopa County?
AQUALIS helps property owners and HOAs across both jurisdictions maintain drainage facilities to the standards Phoenix requires, prepare for Maricopa County’s post-construction BMP inspections, and design retention systems that meet the county’s demanding two-hour, 100-year retention requirement.
The information on this page is provided for general informational purposes only and is not legal advice. Regulations change frequently — AQUALIS makes no warranty as to the accuracy or completeness of this content, and any reliance on it is at your own risk. Consult a qualified professional or your local regulatory authority to confirm requirements applicable to your specific property.
