Last Updated 08/11/2026
Honolulu Stormwater Laws & Regulations
The City and County of Honolulu regulations are compliant with the National Pollutant Discharge and Elimination System (NPDES) permit requirements for the Municipal Separate Storm Sewer System (MS4) under NPDES Permit no. HI S000002. The Storm Water Quality Branch of the Department of Facility Maintenance administers the permitting and compliance program in the city and county of Honolulu. All projects are required to have an Erosion and Sediment Control Plan (ESCP) approved by the Director of the Department of Facility Maintenance before any development occurs.
20-3-2 Purpose
The Rules Relating to Water Quality apply to all Development and Land Disturbing Activities within the City and County of Honolulu and establish minimum requirements for the selection, design, implementation and maintenance of best management practices (“BMPs”) to protect the MS4 and Receiving Waters from Pollutants that are associated with land disturbance, surface hardening, and land use activities. The pollutants of concern (“POC”) addressed by these Rules include, but are not limited to, sediment, nutrients, trash, pathogens, pesticides, oil, grease, hazardous waste, toxic waste, metals, and organic compounds. The standards and requirements established by these Rules are not a maximum limit to the design requirements for BMPs. Compliance with the minimum requirements and standards established by these Rules does not guarantee that selected BMPs will meet their pollution control and/or drainage objectives. Land owners, design professionals, developers, and contractors are encouraged to implement BMPs that go beyond that requirements of these Rules and seek the advice of other agencies that are responsible for water quality, pollution control, Receiving Waters, water rights, flood plains, and storm water. Compliance with these rules does not excuse violations of State or Federal law, City Ordinances, or permits issued by Department of Planning and Permitting or other permitting authorities.
20-3-6 Enforcement of Post-Construction Violations.
Violations involving the failure to effectively prevent Pollutant Discharges to the MS4 or Receiving Waters and violations involving the failure to properly use or maintain Permanent BMPs may be enforced by the Director of the Department of Facility Maintenance.
20-3-7 Responsible Parties.
The owner of Real property located within the City and County of Honolulu is absolutely responsible for compliance with these rules and shall be held liable for any violations occurring on, or, arising from, their property. In addition, the Director [of the Department of Facility Maintenance] may hold any person that causes, contributes to, or fails to prevent a violation of these Rules responsible for the violation and any penalties for the same. Where more than one person is deemed responsible for a violation, the Director may cite and penalize each responsible person separately or hold one or more responsible parties jointly and severally responsible for the violation and penalty.
20-3-14 Project Categories for Development.
(a) Trenching Permit Projects. Development that requires a trenching permit but does not require a building, grading, grubbing, or stockpiling permit.
(b) Category 1A Projects. Development that requires a building permit but does not require a grading, grubbing, or stockpiling permit shall be classified as a Category 1A Project if it meets all of the following criteria: (1) Residential single-family or two-family detached Development; (2) The total Disturbed Area for the Project is less than 1,000 square feet; and (3) Land Disturbing activities will not occur on slopes equal to or greater than 15 percent at the Site.
(c) Category 1B Projects. Development with less than one acre of Disturbed Area that requires a building permit but does not require a grading, grubbing, or stockpiling permit and does not meet the Category 1A Project criteria shall be classified as a Category 1B Project. -11-
(d) Category 1C Projects. Development that requires a building permit but is not required to obtain a grading, grubbing, or stockpiling permit shall be classified as a Category 1C Project if it involves a Disturbed Area of one acre or more or requires a NPDES General/ Individual Permit Authorizing Discharges of Storm Water Associated with Construction Activity, issued by the DOH.
(e) Category 2 Projects. Development requiring a grading, grubbing, or stockpiling permit shall be classified as a Category 2 Project if the area of the zoning lot or portion thereof subject to the permit is less than 15,000 square feet for single-family or two-family dwelling uses and less than 7,500 square feet for other uses.
(f) Category 3 Projects. Development requiring a grading, grubbing, or stockpiling permit shall be classified as a Category 3 Project if the area of the zoning lot or portion thereof subject to the permit is 15,000 square feet or more for single-family or two-family dwelling uses, or 7,500 square feet or more for other uses, but where the total area graded or stockpiled upon is less than 15,000 square feet for single-family or two-family dwellings uses and less than 7,500 square feet for other uses.
(g) Category 4 Projects. Development requiring a grading, grubbing, or stockpiling permit shall be classified as a Category 4 Project if the total area including any areas developed incrementally that is to be graded, grubbed, or stockpiled upon is 15,000 square feet or more for single-family or two-family dwelling uses, or 7,500 square feet or more for other uses, or in the event a proposed cut or fill is greater than 15 feet in height for single-family or two-family dwelling uses, or 7.5 feet in height for other uses.
(h) Category 5 Projects. Development requiring a grading, grubbing, or stockpiling permit shall be classified as a Category 5 Project if it involves a Disturbed Area of one acre or more and which require a NPDES General/Individual Permit Authorizing Discharges of Storm Water Associated with Construction Activity issued by the DOH.
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Frequently Asked Questions
Which agency oversees stormwater compliance in Honolulu?
The Storm Water Quality Branch within the Department of Facility Maintenance administers the city and county’s permitting and compliance program, operating under NPDES Permit No. HI S000002 for the municipal separate storm sewer system. Every project has to secure an Erosion and Sediment Control Plan approved by the Department’s Director before any development activity begins.
How does Honolulu classify a development project for stormwater permitting?
The classification hinges mostly on disturbed area and permit type. A small residential build under 1,000 square feet of disturbance on gentle slopes falls under the lightest category, while anything with a disturbed area of an acre or more, or one that needs an NPDES permit for construction discharges, lands in the most heavily regulated categories. Projects requiring grading, grubbing or stockpiling permits get sorted by lot size, with the threshold set at 15,000 square feet for single-family or two-family uses and 7,500 square feet for everything else. Knowing which category a project falls into early shapes exactly what permitting and BMP requirements apply.
Who's liable for a stormwater violation on Honolulu property?
The property owner is absolutely responsible for compliance, regardless of who actually caused the violation, and can be held liable for anything occurring on or arising from their land. The Director of the Department of Facility Maintenance can also pursue any other person who caused, contributed to or failed to prevent a violation, and where multiple parties share responsibility, the Director can penalize each one separately or hold them jointly and severally liable.
Does meeting Honolulu's minimum BMP standards guarantee compliance?
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.
