What is Maximum Applied Water Allowance (MAWA)?
California's Model Water Efficient Landscape Ordinance (MWELO), codified at California Code of Regulations Title 23, Division 2, Chapter 2.7, sets a ceiling on how much water a covered landscape project may be designed to use each year. That ceiling is the Maximum Applied Water Allowance (MAWA), expressed in gallons per year. Under Section 492.4, a project applicant calculates MAWA using the site's reference evapotranspiration, the maximum ET adjustment factor MWELO allows, and the landscape area, then must design the landscape so its actual estimated water use (ETWU) doesn't exceed it.
This calculator is California-specific: the ETAF values, the 0.62 conversion factor, and the special-landscape-area treatment all come directly from MWELO and only apply to landscape projects it governs. If you want a general property water budget that isn't tied to any regulation, use the landscape water budget calculator instead.
How this MAWA calculator works
The MAWA formula
California Code of Regulations Title 23, Section 492.4 sets out the MAWA equation, using the maximum ET adjustment factor (ETAF) MWELO allows for the project type.
MAWA (gallons per year)
MAWA = ETo × 0.62 × [(ETAF × LA) + ((1 − ETAF) × SLA)]
LA is the total landscape area, including any SLA within it. 0.62 is the ordinance's own conversion factor from inches of water over an area to gallons.
In metric units, since 1 mm of water over 1 m² is exactly 1 liter, the 0.62 conversion factor isn't needed:
Metric units
MAWA (liters per year) = ETo (mm) × [(ETAF × LA) + ((1 − ETAF) × SLA)]
ETAF: 0.55 or 0.45
Section 492.4 sets the maximum ETAF allowed in the MAWA equation at 0.55 for residential landscape areas and 0.45 for non-residential landscape areas, exclusive of special landscape areas. This calculator uses whichever you select.
Special landscape area (SLA)
MWELO worksheet examples describe special landscape areas as those permanently and solely dedicated to edible plants, recreational areas, or areas irrigated with recycled water. Within the formula, the (1 − ETAF) × SLA term effectively raises SLA's allowance up to a full 1.0 ETAF, on top of the standard rate already counted for it within LA.
When this calculator isn't the right tool
Use a different approach for:
- A property outside California, or a budget not tied to any regulation. See the landscape water budget calculator.
- Estimated Total Water Use (ETWU), your landscape design's own calculated water use to compare against MAWA. See the ETWU calculator.
- A single hydrozone's net or gross irrigation depth once you know its water allowance. See the irrigation water requirement calculator.
MAWA calculation example
A residential project (ETAF 0.55) with a total landscape area of 10,000 sq ft, no special landscape area, at an annual ETo of 43 in:
- ETAF term: (0.55 × 10,000) + (0.45 × 0) = 5,500.
- MAWA: 43 × 0.62 × 5,500 ≈ about 146,630 gallons a year.
The same idea in metric
A non-residential project (ETAF 0.45) with 1,000 m² of landscape area, 100 m² of which is a special landscape area, at an annual ETo of 1,000 mm:
- ETAF term: (0.45 × 1,000) + (0.55 × 100) = 450 + 55 = 505.
- MAWA: 1,000 × 505 = about 505,000 liters a year.
When the whole property is special landscape area
A residential project where SLA equals the full 1,000 sq ft of LA, at 40 in of annual ETo:
- ETAF term: (0.55 × 1,000) + (0.45 × 1,000) = 550 + 450 = 1,000, the same as LA alone.
- MAWA: 40 × 0.62 × 1,000 = about 24,800 gallons a year, the same as using an ETAF of 1.0 for the whole property.
All examples use the exact formula the calculator runs; enter your own project's numbers above for your result.
Practical guidance
Use the ETo value from MWELO's own Reference Evapotranspiration Table (Appendix A) for your city, as Section 492.4 requires, rather than a general ETo figure from another source; MWELO compliance calculations are meant to use that specific table. If your city isn't listed, the regulation directs project applicants to a nearby city in the same reference evapotranspiration zone on the CIMIS Reference Evapotranspiration Zones Map.
Keep landscape area (LA) and special landscape area (SLA) measured consistently: SLA is a portion of LA, not an area to add on top of it. If you're unsure whether part of your project qualifies as SLA, check with your local agency, since MWELO implementation and any additional local requirements can vary by jurisdiction even though the statewide ETAF and formula don't.
Check local requirements. Local agencies may adopt MWELO directly or their own ordinance at least as effective; some add requirements beyond the state model. Confirm the current local ordinance and any application process with your city or county before relying on this calculator for a permit submission.
What changes MAWA
| Factor | Effect | What to check |
|---|---|---|
| Project type | Residential uses a higher maximum ETAF (0.55) than non-residential (0.45). | Confirm which classification applies to your project. |
| ETo value used | MAWA scales directly with ETo; a wrong city or zone changes the result. | Use the MWELO Reference Evapotranspiration Table value for your specific city. |
| Landscape area measured | MAWA scales directly with total landscape area. | Measure the actual area to be landscaped, per the project's site plan. |
| Special landscape area | A larger SLA raises MAWA, since SLA effectively gets a 1.0 ETAF. | Only count area that meets MWELO's definition of SLA. |
| Local ordinance differences | Some local agencies adopt requirements beyond the statewide model. | Confirm with your local agency for permit purposes. |
Frequently asked questions
What is MAWA?
Maximum Applied Water Allowance is the ceiling on how much water a landscape may be designed to use annually under California's Model Water Efficient Landscape Ordinance (MWELO), expressed in gallons per year. It's calculated from reference evapotranspiration, a regulatory ET adjustment factor, the total landscape area, and any special landscape area, per California Code of Regulations Title 23, Section 492.4.
What ETo value should I use?
California Code of Regulations Title 23, Section 492.4 requires using the annual ETo value from the Reference Evapotranspiration Table in MWELO Appendix A for your city, or from a nearby city in the same ETo zone on the CIMIS Reference Evapotranspiration Zones Map if your city isn't listed.
What is ETAF and why is it 0.55 or 0.45?
The ET adjustment factor (ETAF) adjusts reference evapotranspiration for plant factors and irrigation efficiency. Under California Code of Regulations Title 23, Section 492.4, the maximum ETAF allowed in the MAWA calculation is 0.55 for residential landscape areas and 0.45 for non-residential landscape areas, exclusive of special landscape areas.
What counts as a special landscape area (SLA)?
MWELO worksheet examples describe special landscape areas as areas permanently and solely dedicated to edible plants, recreational areas, and areas irrigated with recycled water. These areas get an effective ETAF of up to 1.0 within the MAWA formula rather than the standard 0.55 or 0.45.
Is MAWA the same as ETWU?
No. MAWA is the maximum allowance a landscape design may not exceed; Estimated Total Water Use (ETWU) is the actual calculated water use of a specific landscape design, based on its real plant factors and irrigation efficiency. Under MWELO, a compliant design's ETWU must not exceed its MAWA.
See the ETWU calculator.
Does MAWA apply outside California?
No. MAWA and the ETAF values used here are specific to California's Model Water Efficient Landscape Ordinance. Outside California, use the landscape water budget calculator for a general, non-regulatory property budget instead.
See the landscape water budget calculator.
Where do I find my city's MWELO ETo value?
California Code of Regulations Title 23, Section 492.4 points to the Reference Evapotranspiration Table in MWELO Appendix A, published by the California Department of Water Resources, which lists an annual ETo value for cities across the state.
What if my entire property is a special landscape area?
If special landscape area equals your total landscape area, the ETAF term in the formula cancels out and MAWA simplifies to ETo × 0.62 × landscape area, the same result as using an ETAF of 1.0 for the whole property.
Who built and checked this calculator
Licensed Professional Engineer and Irrigation Association Certified Irrigation Designer with more than 20 years in irrigation design, system auditing and landscape water management. Full profile
How this page was checked
- The MAWA formula and both worked examples were verified by hand, including the special-landscape-area identity check, and traced against the code.
- ETAF values (0.55 / 0.45) and the MAWA formula were checked against the current California Code of Regulations text and cross-checked against multiple current local ordinances implementing MWELO.
- The page states clearly, per the brief's watch item, that this tool is California-specific.
Sources
- California Code of Regulations, Title 23, Division 2, Chapter 2.7. Section 492.4, Water Efficient Landscape Worksheet (MAWA formula, ETAF values, ETo table requirement).
- California Department of Water Resources. Model Water Efficient Landscape Ordinance, Regulatory Text.
- City of San Mateo Municipal Code. 23.72.070, Water Budget Calculations (current local implementation of the statewide MAWA formula).
- City of Woodland. MWELO Worksheet Example (worked MAWA formula notation).