Paramount, CA Landscaping Rules: Rainwater Harvesting (2026)

In Paramount's code, rainwater harvesting lives inside the stormwater chapter. Section 8.20.010 defines "Rainfall harvest and use" as a LID BMP system designed to capture runoff, from a roof or from elsewhere within the site, and to provide temporary storage until the harvested water can be used for irrigation or non-potable uses. Potable use is allowed only if the system includes disinfection treatment and is approved for such use by the local Building Department.

Section 8.20.210 applies the idea to planning priority projects: the site must be designed to control pollutants, pollutant loads and runoff volume to the maximum extent feasible by minimizing impervious surface area and controlling runoff through infiltration, evapotranspiration, bioretention and/or rainfall harvest and use. Covered projects include development of one acre or greater of disturbed area that adds more than 10,000 square feet of impervious surface, industrial parks and commercial malls with 10,000 square feet or more of impervious surface, and street and road construction of 10,000 square feet or more. Retail gasoline outlets, restaurants, parking lots and automotive service facilities are covered at 5,000 square feet or more of impervious surface, and parking lots are also covered at 25 or more spaces. Existing single-family dwellings and accessory structures are exempt from the redevelopment requirements unless the project creates, adds or replaces 10,000 square feet of impervious surface area.

The benchmark is the Stormwater Quality Design Volume, the runoff from the 85th percentile 24-hour event or from a 0.75 inch, 24-hour rain event, whichever is greater. An applicant claiming technical infeasibility must show the project cannot reliably retain 100% of that volume on site, even with the maximum application of green roofs and rainwater harvest and use, through a site-specific analysis endorsed by a registered professional. The LID plan is prepared by a registered civil engineer, licensed architect, landscape architect or other professional knowledgeable about stormwater quality, maintenance records for structural BMPs are kept for three years, and the signed plan is filed with the County Recorder and binds successors in interest.