Distribution Uniformity Calculator

Score Interpretation

0.75+ (Excellent): Your system is performing well. Minimal water waste from non-uniformity. Adjusted run times add less than 33% extra water.

0.65 – 0.74 (Good): Acceptable for most applications. Some dry spots may exist but overall performance is reasonable. Consider fine-tuning head alignment and pressure.

0.55 – 0.64 (Fair): Significant non-uniformity. You are applying 56–82% more water than necessary to cover the driest spots. Consider nozzle replacement, pressure regulation, or head spacing adjustment.

Below 0.55 (Poor): Major design or maintenance issues. A system audit is recommended. You may be doubling your water use just to keep dry spots alive.

Common Causes of Poor DU

Mismatched nozzle sizes — Different nozzles in the same zone apply water at different rates, creating wet and dry spots.

Low or variable pressure — Sprinkler heads are designed for a specific pressure range. Outside that range, the spray pattern distorts.

Head spacing too wide — Spacing beyond the manufacturer's recommendation leaves gaps in coverage (head-to-head spacing is ideal).

Tilted or sunken heads — Heads that aren't level throw water unevenly. Sunken heads get blocked by turf.

Wind during testing — Wind distorts spray patterns and makes results unreliable. Retest on a calm day (wind < 5 mph).

Clogged nozzles — Partial blockages reduce flow and distort patterns. Inspect and flush nozzles regularly.

How to Run a Catch Can Test

1. Place catch cans in a grid pattern within a single irrigation zone. Use identical cans (straight-sided containers like tuna cans work in a pinch).

2. Space cans evenly, typically 5–10 ft apart depending on head spacing. The grid should cover the full zone.

3. Run the zone for a measured time. 15 to 30 minutes is typical. Record the exact duration.

4. Measure the volume in each can using a graduated cylinder or the can's markings. Record in milliliters or fluid ounces.

5. Enter the data in the grid above. The calculator handles the rest.

What is distribution uniformity (DU)?

Distribution uniformity is a measure of how evenly an irrigation system applies water across a zone. It is calculated using the lower-quarter method: the average volume collected in the lowest 25% of catch cans divided by the overall average. A DU of 1.0 means perfectly uniform application. Most well-maintained commercial systems achieve 0.65–0.80. DU is the single most important metric from a catch can audit because it directly determines how much extra water you must apply to keep dry spots alive.

How often should I run a catch can test?

At minimum, test each zone once per year. Retest after any maintenance that affects water distribution: nozzle replacement, head adjustment, pressure changes, or adding/removing heads. Golf courses typically test each area seasonally. If you notice new dry spots or wet areas, test immediately: something has changed. Testing after installation or renovation is essential to establish a baseline DU for each zone.

What is a good DU score for a golf course?

Golf courses should target a DU of 0.70 or higher for fairways and 0.75+ for greens and tees. A DU below 0.65 on a golf course results in visible dry spots or excessive overwatering to compensate. Top-performing courses achieve 0.80+ through proper head-to-head spacing, matched precipitation rate nozzles, and pressure regulation. Courses in windy areas may see lower field DU than the design specification suggests.