California MWELO Irrigation Audit SOP

Why this matters

California's Model Water Efficient Landscape Ordinance (MWELO) is the binding state-level rule for irrigation system design, installation, and audit on any new or rehabilitated landscape over the threshold defined in California Code of Regulations Title 23, Division 2, Chapter 2.7. MWELO covers residential rehabilitated landscapes over 2,500 sq ft and new residential landscapes over 500 sq ft, plus commercial thresholds. Local water purveyors (water districts and municipal water departments) enforce MWELO and have stop-work and refund authority on noncompliant landscapes. A lawn care firm operating in California has to deliver MWELO-compliant audits as part of irrigation work on these jobs, or risk the customer's project getting flagged at certificate-of-occupancy or at the local water agency's audit cycle. This SOP walks the audit workflow.

Step 1 - Confirm the project is subject to MWELO

MWELO applies to:

• New construction landscapes of 500 sq ft or greater (residential) or 2,500 sq ft (commercial / multifamily).
• Rehabilitated landscapes equal to or greater than 2,500 sq ft requiring a permit, plan check, or design review.
• Existing landscapes 5,000 sq ft or greater that are subject to a public water agency's audit cycle.

Confirm the local water purveyor has not adopted a more stringent local ordinance. Cities and water districts can adopt local rules stricter than the state MWELO but cannot be more lenient. Check with the customer's water utility before scoping the audit.

Step 2 - Pull the Landscape Documentation Package

For a new or rehabilitated project, the original Landscape Documentation Package should be on file with the local water purveyor. The package includes the Water Efficient Landscape Worksheet (water budget calculation), Soil Management Report, Landscape Design Plan, Irrigation Design Plan, and Grading Design Plan if applicable. The audit is a comparison of the installed system against the approved design documents. Without the package, the audit is a baseline assessment instead of a compliance audit.

Step 3 - Calculate the Maximum Applied Water Allowance (MAWA)

The MAWA is the upper limit on annual water use for the landscape, calculated from:

• ETo (reference evapotranspiration) for the local climate zone, from the CIMIS station or the CCR Title 23 Appendix A ETo table.
• ETAF (Evapotranspiration Adjustment Factor): 0.55 for residential, 0.45 for commercial.
• Landscape Area in square feet.
• 0.62 conversion factor for gallons per square foot per inch of water.

MAWA (gallons per year) = ETo (inches per year) x ETAF x Landscape Area (sq ft) x 0.62

The Estimated Total Water Use (ETWU) of the installed system - computed from hydrozone areas, plant water use factors, irrigation efficiency, and special landscape area allowances - must be at or below the MAWA. Document both numbers and the calculation in the audit report.

Step 4 - Inspect the irrigation system against the design plan

The on-site inspection compares the installed system to the irrigation design plan. Walk every hydrozone with the design plan in hand. Verify:

• Hydrozones are physically separated and on separate valves (high-water-use plants on one valve, low-water-use plants on another, turf on its own valve).
• Drip and low-flow micro-irrigation is used for non-turf areas under MWELO Section 492.7(a)(1)(F).
• No overhead irrigation in any area less than 10 feet wide under Section 492.7(a)(1)(B).
• Smart irrigation controller installed - either weather-based (WBIC) or soil moisture-based (SMS), listed by the EPA WaterSense program.
• Master shutoff valve installed at the meter.
• Pressure regulation at the controller or at each valve where required.
• Check valves on heads to prevent low-head drainage.
• Rain sensor or weather-based controller override functional.

Photograph each finding. Note discrepancies between the installed system and the design.

Step 5 - Run a distribution uniformity (DU) test on each turf zone

For turf zones, run a catch can test per ANSI/ASABE S526 and IA (Irrigation Association) audit protocols. Place catch cans on a grid across the zone, run the zone for a fixed duration, measure the volume in each can. Calculate the Lower Quarter Distribution Uniformity (DU_lq):

DU_lq = (average of the lowest quarter of catch can volumes) / (average of all catch can volumes)

A DU_lq of 0.70 or greater is the IA-recommended threshold for turf rotor systems; 0.65 for spray systems. Below 0.65, the system is over-applying water in some areas and under-applying in others, and the zone needs head-spacing, head-rotation, or pressure correction before the system is signed off as MWELO-compliant.

Step 6 - Audit the controller programming

Open the controller and document:

• Each program's run time and frequency.
• Whether the controller is in seasonal-adjust mode and what the current seasonal adjust is set to.
• Rain sensor or weather-based feed status.
• Smart features active (ET-based, soil-moisture based, cycle-and-soak).

Compare programmed run times against the hydrozone water requirement at current ET. Run times that exceed the requirement for the hydrozone are flagged for adjustment. Run times that under-apply for the hydrozone are also flagged - under-irrigation is a noncompliance under MWELO Section 492.10.

Step 7 - Document the audit report

The MWELO audit report contains: project identification, address, water meter number, water purveyor; MAWA calculation with ETo source and ETAF used; ETWU calculation with hydrozone breakdown; system inspection findings with photos; distribution uniformity test results per zone; controller programming documentation; findings of noncompliance with specific MWELO section citations; recommended corrections and re-audit timeline. Submit to the customer and, where required by the local water purveyor, file a copy with the agency.

Step 8 - Track re-audit and ongoing compliance

For commercial and multifamily landscapes 5,000 sq ft or greater, MWELO requires periodic re-audits on the cycle the local water purveyor adopts (typically every five years). For drought-cycle response, the State Water Resources Control Board has issued emergency regulations during prior droughts (2014 to 2017, 2021 to 2023) that further restricted outdoor irrigation - the local purveyor's website is the source of truth on current drought-cycle rules.

References

1. California Code of Regulations Title 23, Division 2, Chapter 2.7 (Model Water Efficient Landscape Ordinance, MWELO)
2. California Department of Water Resources, MWELO Guidebook and Implementation Resources
3. EPA WaterSense Specification for Weather-Based Irrigation Controllers
4. ANSI/ASABE S526.4, Soil and Water Terminology (Irrigation Auditor reference)
5. Irrigation Association (IA), Certified Landscape Irrigation Auditor (CLIA) curriculum and audit protocol
6. California State Water Resources Control Board, Emergency Drought Regulations (referenced under historical drought response)