Irrigation Audit Glossary

A measure of how evenly water is distributed across an irrigation zone, expressed as a percentage from 0 to 100.

DU is calculated by dividing the average of the lowest quartile of catch-can volumes by the overall average. A DU of 75% or above is considered acceptable for spray heads. Below 50% indicates significant uniformity problems that waste water and create dry spots. DU testing is the foundation of IA Standard irrigation audits.

A field test that measures water distribution uniformity by placing collection containers in a grid pattern across an irrigation zone.

Catch cans (or cups) are placed at regular intervals, the irrigation zone runs for a fixed time, and the water collected in each can is measured. The data is used to calculate Distribution Uniformity (DU) and precipitation rate. The Irrigation Association recommends a minimum of 16-24 cans per zone for statistically valid results.

The rate at which an irrigation system applies water to the landscape, measured in inches per hour.

Precipitation rate is calculated by dividing the average catch-can volume by the test duration and converting to inches per hour. Matched precipitation rates across zones on the same valve are critical — mismatched rates cause overwatering in some areas and underwatering in others. Typical spray head rates range from 1.0 to 2.0 in/hr, while rotors range from 0.4 to 0.8 in/hr.

The maximum amount of water that may be applied to a landscape under California's MWELO regulation, measured in gallons per year.

MAWA is calculated as: MAWA = (ETo × 0.55 × LA × 0.62) for residential, or (ETo × 0.45 × LA × 0.62) for non-residential landscapes. ETo is the reference evapotranspiration for the site, LA is the total landscape area in square feet, and 0.62 converts acre-inches to gallons. A landscape is compliant when its ETWU does not exceed its MAWA.

The estimated annual water use of a landscape based on its plant types, irrigation efficiency, and climate zone.

ETWU is calculated per hydrozone as: ETWU = (ETo × PF × HA × 0.62) / IE, where PF is the plant factor from WUCOLS, HA is the hydrozone area, and IE is the irrigation efficiency (typically 0.75 for spray, 0.81 for drip). The sum of all hydrozone ETWUs gives the total landscape ETWU, which must not exceed the MAWA for MWELO compliance.

California's state regulation requiring water-efficient landscaping for new and renovated landscapes over 500 square feet.

MWELO was first adopted in 2009 and significantly updated in 2015. It establishes water budgets (MAWA) for landscapes and requires that estimated water use (ETWU) not exceed the budget. It applies to all new construction and rehabilitated landscapes in California. Local agencies may adopt more stringent ordinances. CLCA irrigation audits document MWELO compliance.

An irrigation audit methodology certified by the California Landscape Contractors Association (CLCA) that documents MWELO compliance through hydrozone analysis.

A CLCA audit divides the landscape into hydrozones (areas with similar water needs), calculates ETWU for each zone using WUCOLS plant factors, and compares the total against the MAWA budget. The audit produces documentation accepted by California water agencies as proof of compliance. CLCA audits are required for many commercial and municipal landscape projects in California.

An irrigation audit methodology developed by the Irrigation Association (IA) based on catch-can distribution uniformity testing.

The IA Standard audit follows the procedures outlined in the IA Landscape Irrigation Auditor handbook. It involves catch-can DU testing, precipitation rate calculation, scheduling coefficient analysis, and ET-based runtime recommendations. IA Certified Landscape Irrigation Auditors (CLIA) are trained in this methodology.

A 0-100 point score that quantifies the overall condition of an irrigation system based on documented findings.

The score starts at 100 and deducts points for each finding based on severity: Minor findings deduct 2 points, Moderate findings deduct 5 points, and Critical findings deduct 10 points. Multiple findings of the same type have diminishing deductions. A score of 85+ is Good, 70-84 is Fair, and below 70 is Poor. The score provides a simple, comparable metric for tracking system condition over time.

Unexpected water flow detected at a meter when no irrigation zones are actively running, indicating underground leaks or stuck valves.

Ghost flow is detected during metered flow audits by reading the water meter when all zones are shut off. Any flow registered on the meter indicates water is leaking somewhere in the system. Common causes include cracked mainlines, stuck zone valves, weeping check valves, and underground lateral breaks. Ghost flow can waste thousands of gallons per month without any visible surface indication.

An area of a landscape grouped by plants with similar water requirements, microclimate exposure, and soil conditions.

Hydrozones are the fundamental unit of CLCA/MWELO water budget calculations. Each hydrozone has a plant factor (from WUCOLS) that determines its water needs relative to reference evapotranspiration. Proper hydrozone grouping is essential for efficient irrigation — mixing high-water and low-water plants in the same zone forces overwatering of drought-tolerant species.

A coefficient from 0.1 to 0.9 that indicates a plant species' water needs relative to reference evapotranspiration (ETo).

Plant factors are published in the WUCOLS (Water Use Classification of Landscape Species) database maintained by the University of California. Low-water plants (e.g., native grasses) have PFs of 0.1-0.3, moderate-water plants (e.g., most shrubs) have PFs of 0.4-0.6, and high-water plants (e.g., cool-season turf) have PFs of 0.7-0.9. These factors are used in ETWU calculations.

The amount of water lost through evaporation and plant transpiration from a standardized reference surface, measured in inches per year.

ETo varies by climate zone and is published by CIMIS (California Irrigation Management Information System) and similar agencies in other states. It represents the baseline water demand for a well-watered grass surface. Actual landscape water needs are calculated by multiplying ETo by plant factors and area. Higher ETo values mean hotter, drier climates with greater irrigation demand.

The ratio of water beneficially used by plants to the total water applied by the irrigation system.

IE accounts for losses from overspray, wind drift, runoff, and deep percolation. Standard efficiency values used in MWELO calculations are 0.75 (75%) for spray systems and 0.81 (81%) for drip systems. Actual efficiency can be measured through catch-can testing. Higher DU generally correlates with higher irrigation efficiency.

An irrigation audit that measures actual water flow through the meter for each zone and compares it against expected baselines and budget targets.

Metered flow audits record GPM (gallons per minute) for each zone by reading the water meter while zones run individually. This data is used to detect ghost flow, validate zone flow rates against design specs, calculate weekly and annual water consumption, and model watering scenarios. Budget tracking compares actual consumption against annual water budgets with tier pricing threshold alerts.

A modeled irrigation schedule that projects water consumption under different conditions such as Full, Water Saver, Survivability, or Custom runtimes.

Scenarios allow auditors to show clients how much water and money they can save by adjusting runtimes. The Full scenario uses design-intent runtimes, Water Saver reduces by a percentage, and Survivability uses the minimum to keep plants alive. Custom scenarios allow per-zone runtime overrides. Each scenario calculates weekly gallons, annual gallons, and cost at the applicable water rate.