catch can size
volume collected
catch can volumes (ml) — highlighted cans = lowest quarter
What is distribution uniformity?
DU measures how evenly water is distributed across a zone. It's the ratio of the lowest quarter of catch can readings to the overall average, expressed as a percentage.
DU benchmarks
Excellent: 85%+. Good: 75–85%. Fair: 65–75%. Poor: below 65%. Most residential systems run 55–70% — significant room for improvement through head adjustment and nozzle replacement.
How to set up a catch can test
Place cans evenly across the zone in a grid pattern. Run the zone for 15–30 minutes, collect and measure each can in ml, then enter the volumes above.
Common causes of low DU
Worn nozzles, misaligned heads, mixed head types in one zone, pressure variation, or poor original design. A DU below 65% warrants a full audit.
Catch can test explained
What's the formula?
PR (mm/hr) = (volume collected in ml ÷ catch can area in cm²) × 10 × (60 ÷ test duration in minutes). The ×10 converts cm to mm, and the 60÷duration scales to an hourly rate.
How is DU calculated?
Distribution Uniformity (DU) = (average of the lowest 25% of readings ÷ overall average) × 100. The lowest quarter represents the driest parts of the zone — the areas that will be underwatered if you set run times based on the average.
How many catch cans do I need?
For a meaningful DU result, use at least 4 cans — ideally one near each head and one between heads. For a large commercial zone, 9–16 cans in a grid gives a more accurate picture. More cans always means a more reliable DU score.
What should I do with a low DU result?
First check head alignment — many low DU scores are simply from heads that have been knocked out of position. Then check for worn nozzles and pressure variation. If the system was originally designed with mixed head types in a zone, a redesign may be the only real fix. Contact Retic Man for a professional zone audit across Perth.
Need to measure pipe flow rate instead?
The catch can test measures how much water your sprinklers are putting down. If you want to measure actual pipe flow — useful for pump selection or zone sizing — use the Bucket Flow Test tool instead.