The California MWELO ordinance (Model Water Efficient Landscape Ordinance) is the design rulebook every landscape architect, designer, and installer working on new and rehabilitated landscapes in the state must follow. Codified in California Code of Regulations Title 23, Division 2, Chapter 2.7, MWELO sets binding water-use budgets, irrigation efficiency thresholds, plant-factor caps, and soil and mulch requirements for projects above stated size thresholds. With SB 1157 now layered on top, MWELO is the operating manual for what gets installed in the first place.
The short version
- MWELO applies to new residential landscape installs over 2,500 sq ft, rehab projects over 1,200 sq ft, and CII projects over 500 sq ft (varies by jurisdiction).
- The cornerstone is the Estimated Total Water Use (ETWU) calculation, which must come in at or below the Maximum Applied Water Allowance (MAWA).
- WUCOLS plant factor of 0.3 or lower is the standard for low-water plant selection.
- Irrigation efficiency must be 75 percent or higher (drip and microspray) and 80 percent for high-efficiency overhead.
- Mulch depth requirement is 3 inches minimum on all exposed soil surfaces.
- Local agencies adopt MWELO as a baseline and many add stricter requirements on top.
What the rule says
MWELO was adopted by the California Department of Water Resources in 2009 and substantially revised in 2015 (the version most jurisdictions use today). The ordinance is “model” in name because each city or county must adopt a local version that is at least as strict as the state baseline. Most jurisdictions adopted MWELO verbatim, but some (San Francisco, Marin Municipal Water District, several Orange County cities) added stricter plant-palette and irrigation-controller requirements.
Applicability thresholds are the first thing every designer needs to know. New residential landscapes of 2,500 square feet or more (including the landscape area on building permits) trigger the full ordinance. Residential rehab projects of 1,200 square feet or more trigger it. CII (commercial, industrial, institutional) projects trigger at 500 square feet in most jurisdictions, with some pulling that threshold to zero for any new install. Smaller residential projects are subject to a prescriptive compliance pathway with simpler documentation, but still must meet the core plant factor and irrigation efficiency limits.
The ETWU and MAWA calculations are the heart of the ordinance. MAWA is computed as ETo (the reference evapotranspiration for the local climate zone) multiplied by a conversion factor (0.62), multiplied by the landscape area, multiplied by an evapotranspiration adjustment factor (0.55 for residential, 0.45 for nonresidential). ETWU is the projected actual water use based on the plant palette, hydrozone areas, plant factors, and irrigation efficiencies. The designer must show ETWU is less than or equal to MAWA. The math is run on a landscape documentation package submitted with the building permit.
Plant factors come from WUCOLS (Water Use Classification of Landscape Species), the University of California Cooperative Extension reference. Low-water plants carry a plant factor of 0.0 to 0.3, moderate of 0.4 to 0.6, and high of 0.7 to 0.9. MWELO does not ban high-water plants outright but caps the weighted average at the MAWA-equivalent through the ETWU math. In practice, most compliant designs use a plant palette weighted toward 0.3 or lower.
Irrigation efficiency thresholds require drip and microspray systems to achieve 75 percent efficiency or higher, and high-efficiency overhead sprinklers (matched precipitation rate rotors and rotary nozzles) to hit 80 percent. Standard fixed-spray heads cap at 70 percent and are essentially disqualified for most MWELO designs. Smart controllers with weather-based or soil-moisture sensors are required on all new installs.
Soil and mulch requirements close out the prescriptive section. Compacted soils must be amended with a minimum of 6 cubic yards of compost per 1,000 square feet, tilled to a depth of 6 inches. All non-turf planting areas must be top-dressed with a minimum of 3 inches of mulch.
Why it matters for designers and installers
MWELO is the gatekeeper for every permitted residential and commercial install in California, which means it is also the gatekeeper for a multi-billion-dollar slice of the design-build market. Projects that fail MWELO review get bounced at plan check, which can delay permit issuance by 30 to 90 days and force redesigns that wipe out project margin. Most jurisdictions now require a stamped landscape architect or certified designer signature on the MWELO compliance package.
For installers and contractors, the practical effect is that plant palettes have shifted dramatically over the last decade. Spec plant lists from 2010 (heavy on hybrid bermuda, Indian hawthorn, Japanese boxwood, photinia) have been replaced by lists that lean on California natives, Mediterranean-climate Australians and South Africans, agaves and succulents, and a much shorter list of low-water turf alternatives. The contractors who win in 2026 are the ones with deep grower relationships for low-water plants and crews trained on drip and microspray installation. See our drought-tolerant lawn alternatives guide and drip irrigation install guide for the operational playbooks.
Inspections matter. MWELO requires both a pre-installation inspection (verifying soil prep and irrigation rough-in) and a final inspection (verifying plant placement, mulch depth, and controller programming). Failed inspections force corrections at the contractor’s expense. The most common fail points are insufficient mulch depth, irrigation controller programming that ignores hydrozone separation, and plant counts that fall short of MWELO documentation.
What designers, installers, and property owners should do
For designers, the MWELO worksheet (the DWR-published spreadsheet, updated as recently as 2023) is the single most important document. Run the ETWU and MAWA math on every project that triggers applicability. Build a default plant palette library weighted toward WUCOLS 0.0 to 0.3 species for your climate zone. Default to drip and microspray for shrub and groundcover areas; reserve high-efficiency overhead only for turf areas where overhead is genuinely the right call.
For installers, train field crews on three details that fail inspection most often: mulch depth (3 inches minimum, measured after settling), drip line layout (emitters within 12 inches of every plant root zone), and controller programming (zone separation by hydrozone, not by manifold convenience). Document everything with date-stamped photos.
For property owners, ask for a copy of the MWELO compliance package at project handoff. It is the legal record of what was installed and how it was designed to perform. If you sell the property, the package transfers with the title for the local jurisdiction’s water-budget billing. For commercial properties, the package is often required for tenant improvement permits.
By the numbers
| Requirement | Threshold |
|---|---|
| Applicability, new residential install | 2,500 sq ft and above |
| Applicability, residential rehab | 1,200 sq ft and above |
| Applicability, CII new install | 500 sq ft and above (varies by jurisdiction) |
| WUCOLS low-water plant factor | 0.0 to 0.3 |
| ET adjustment factor, residential | 0.55 |
| ET adjustment factor, nonresidential | 0.45 |
| Drip and microspray efficiency | 75% minimum |
| High-efficiency overhead efficiency | 80% minimum |
| Mulch depth, non-turf areas | 3 inches minimum |
| Soil amendment, compacted areas | 6 cu yd compost per 1,000 sq ft |
Background and context
The original 1992 Water Conservation in Landscaping Act required DWR to publish a model ordinance and required local agencies to adopt either the state model or an equivalent. The 2009 first major revision tightened the ETWU math and brought in WUCOLS. The 2015 revision, triggered by Governor Brown’s emergency drought executive order, dropped the residential applicability threshold from 5,000 to 2,500 square feet, added the CII category, brought rehab projects into the rule, and tightened irrigation efficiency requirements. The 2023 worksheet update reflected updated WUCOLS data and the addition of new low-water species to the recommended palettes.
MWELO sits inside a stack of California landscape water rules that includes SB 1157 (the non-functional turf ban), the urban water supplier conservation framework, and the 2018 indoor water-use standard. Together they form what DWR calls the “make conservation a California way of life” regulatory package. SB 1157 picks up where MWELO leaves off: MWELO governs what you can install, SB 1157 governs what existing landscapes can still irrigate.
FAQ
Does MWELO apply to my home remodel if I am only redoing the front yard?
It depends on size. If the rehab project disturbs 1,200 square feet or more of landscape area, full MWELO applies. Below that, the prescriptive compliance pathway applies (simpler documentation, but the plant factor and irrigation efficiency requirements still apply).
Can I still install turf under MWELO?
Yes, but the ETWU math will be tighter. Turf carries a plant factor of 0.7 to 0.8, which means a high turf-area share will push ETWU close to or above MAWA. Most MWELO-compliant residential designs limit turf to 25 percent or less of the total landscape area, often as a single recreation panel. Functional turf is allowed under both MWELO and SB 1157.
Who reviews the MWELO compliance package?
The local building or planning department, sometimes with input from the local water supplier. Some cities have dedicated landscape plan checkers; others run the review through their building plan check team.
What happens if my project fails MWELO review?
The permit will not issue, or a conditional permit will issue with redesign requirements. Common fixes include reducing turf area, swapping high-water plants for low-water alternatives, upgrading the irrigation controller, or adding mulch to non-turf areas.
Are there exemptions?
Agricultural areas, registered historic landscapes, cemeteries, and athletic fields are exempt. Edible gardens and food production areas are exempt from the plant factor requirements (but still must use efficient irrigation).
Bottom line
MWELO is not new and it is not optional. Every designer and installer working on permitted residential or commercial projects in California should treat it as the operating standard, and every property owner planning a new install or rehab should ask for the compliance package at handoff. Stack it with SB 1157 and the 2026 rebate programs for the full California water regulatory picture. For the design playbook on what to plant inside the MWELO envelope, see drought-tolerant lawn alternatives and the 2026 yard design guide.