Merced County, CA Landscaping Rules: Rainwater Harvesting (2026)

030(A)(3)(a) requires 'small development projects,' those that create or replace, including projects with no net increase in impervious surface, between 2,500 and 5,000 square feet of impervious surface, including detached single-family homes crossing the 2,500-square-foot threshold that are not part of a larger plan of development, to implement one or more of seven listed site design measures to reduce project runoff. Rooftop and Impervious Area Disconnection is listed as option (iv): rerouting rooftop drainage pipes to rain barrels, cisterns, or on-site permeable areas instead of the storm drain system.

The other six options are stream setbacks and buffers, soil quality improvement, tree planting and preservation, porous pavement or concrete, green roofs, and vegetated swales. A project proponent choosing rooftop disconnection, or any other measure, must quantify the resulting runoff reduction using the State Water Board's SMARTS Post-Construction Calculator or another methodology the county accepts. 030(B) rather than this small-project menu. The chapter does not require rain barrels on every house; it is one compliance path among several, and only for qualifying projects within the 2,500-to-5,000-square-foot band. The department of public works administers and reviews the chosen measures as part of civil plan review for the project.