SONOMA COUNTY -- Starting Friday, new or revised landscaping for commercial buildings and homes in the unincorporated areas of Sonoma County will need to comply with new rules on water efficiency adopted recently.

The Water Efficient Landscape Ordinance, developed by a group of businesses and public agencies and adopted by the Board of Supervisors on Dec. 15, applies to users of public water systems and groundwater. It requires landscape plan checks and inspections for commercial and industrial buildings, wineries, apartment complexes, new homes and residences with additions larger than 400 square feet.

It limits landscape irrigation to 60 percent of the water required by a similar-sized landscape composed entirely of lawn, a measurement of plant water demand called evapotranspiration, or ETo.

That's more restrictive than the model statewide ordinance part of the Water Conservation in Landscaping Act of 2006, or Assembly Bill 1881, according to county planner Amy Wingfield. Local land-use agencies were supposed to adopt a form of the model ordinance, which limits irrigation to 70 percent of turf water use, by Jan. 1.

"Because our area receives significantly higher rainfall amounts than other areas of the state, the stakeholder group felt our regional ordinance could require a more restrictive water budget," wrote Ms. Wingfield in a report for the board in December.

Sonoma County's new ordinance requires landscape plans with water budgets, prevention of excessive erosion and irrigation runoff, a soil-management report including soil amendments and mulching, landscape and irrigation design, irrigation audits, scheduling of irrigation based on the local climate and any needed grading plan.

Ordinance exemptions include home landscapes smaller than 5,000 square feet, designs with less than 600 square feet of turf and systems with a weather-based irrigation controller.

For more information, contact Ms. Wingfield at 707-565-7389 or awingfie@sonoma-county.org or read the ordinance at www.sonoma-county.org/prmd/docs/landscape_ord/index.htm.