Measure delivery from one operating zone
A catch-cup test measures water arriving at different places during the same sprinkler run. It helps distinguish average application from uneven delivery. Use it to record system performance before deciding whether a runtime change addresses the problem.
Inspect obvious leaks, blocked heads and misalignment first. For a full home-lawn audit, New Mexico State University calls for at least 24 uniform catch cans. Test in calm conditions and follow the audit’s placement method. Four selected cans are not a substitute for that full-zone sample.
Run the test and preserve every reading
- Sketch the zone and number the can locations. Use level containers with a consistent collecting area and distribute them according to the audit procedure.
- Record the operating zone, wind conditions and test duration. Run long enough for readable catches without overflow.
- Read every container consistently and record zero catches as zero. If reading volume instead of depth, account for the container’s collecting area.
- Record runoff, obstructions and abnormal head behavior. Save the raw readings so a later test uses comparable locations and conditions.
Calculate rate and uniformity separately
Average application rate is mean collected depth ÷ run minutes × 60, in inches per hour. It describes how quickly this test applied water on average. It does not establish how much water the lawn needs.
Lower-quarter distribution uniformity compares the average of the lowest quarter of catches with the average of all catches. The site calculator accepts four depths, so its lowest quarter is just the single lowest reading. Treat its output as a simplified four-sample diagnostic, not a full irrigation audit.
Enter all four depths in inches and a positive duration in minutes. Depths cannot be negative. If every catch is zero, the application rate is zero and a uniformity ratio is undefined because the mean is zero. Investigate the system rather than interpreting an undefined ratio as good performance.
| Output | Calculation | What it answers |
|---|---|---|
| Mean depth | Sum of depths ÷ number of catches | How much water the sample received on average. |
| Application rate | Mean depth ÷ minutes × 60 | How fast water was delivered during the test. |
| Four-sample ratio | Lowest depth ÷ mean of all four depths | How the lowest of these four samples compares with their mean. |
| Full lower-quarter uniformity | Mean of the lowest quarter ÷ mean of the full audit | How the low-water part of a correctly sampled zone compares with the whole. |
Worked example: the calculator’s four-sample diagnostic
- Inputs
- A 15-minute test records depths of 0.25, 0.30, 0.35 and 0.30 in.
- Calculation
Mean: (0.25 + 0.30 + 0.35 + 0.30) ÷ 4 = 0.30 in. Ratio: 0.25 ÷ 0.30 = 0.833333… . Rate: 0.30 ÷ 15 × 60 = 1.20 in/hr.- Result
- 0.83 ratio (about 83.33%) and 1.20 in/hr
The tool displays a ratio, not a percentage, and rounds it to two decimal places. The percentage here uses the unrounded ratio. These four samples illustrate the tool; use the complete procedure for a full audit.
Use the result to guide the next check
An acceptable average can coexist with dry patches. Repair distribution problems before assuming that more runtime is the answer. Use local plant needs, weather and effective rainfall to choose a watering target; the test only measures delivery.
Keep the test record and repeat it after relevant repairs. Do not enter four favorable readings from a larger audit and call the result the uniformity of the full zone.
- Zone sketch and all can positions
- Space to write when printed
- Date, wind and operating conditions
- Space to write when printed
- Container type, collecting area and units
- Space to write when printed
- Measured test duration
- Space to write when printed
- Every catch, including zeros
- Space to write when printed
- Calculated rate, sample limitations and repairs
- Space to write when printed
Conclusion
Keep all measurements, separate delivery rate from uniformity and interpret each result within its sampling limits. Use a suitable watering target and repair evidence together when reviewing runtime.