Test Sprinkler Coverage – Complete Guide 2026

You cannot tell if your sprinklers are covering the lawn evenly just by looking. The grass all looks green while the sprinklers run. But a week later, brown spots appear where coverage was weak. Testing your sprinkler system coverage catches these problems before the lawn suffers. Here is exactly how to do it.

What You Need

Catch cups or tuna cans. You need at least 10 to 15 identical containers. Tuna cans work perfectly. They are exactly 1 inch tall. Rain gauges or small straight-sided cups also work. Just make sure every container is identical. A ruler to measure water depth. A notebook and pen to record results. About an hour of time.

Step 1: Place the Catch Cups in a Grid

Place containers in a grid pattern across the zone you are testing. Space them about 5 to 10 feet apart. Place more containers where coverage might be weak. Near the edges of the spray pattern. Between two sprinkler heads. In corners. Behind shrubs or obstacles.

Important: Place containers in the overlap areas between heads. Head-to-head coverage is where most problems hide. If two heads are supposed to overlap their spray, place containers in the overlap zone.

Label or number each container and mark its location on a sketch of your lawn. You need to know which container was where when you analyze the results.

Step 2: Run the Zone for a Set Time

Run the sprinkler zone for exactly 15 minutes. Use a timer. Do not guess. Exactly 15 minutes. If the weather is windy, wait for a calm day. Wind ruins the test by blowing water into some containers and away from others.

If you are testing multiple zones, test one zone at a time. Overlapping spray from different zones will give you false readings.

Step 3: Measure and Record

After 15 minutes, turn off the water. Go container to container. Measure the water depth in each with your ruler. Record the measurement next to the container number on your sketch. Measure in fractions of an inch. Write everything down.

Calculate the average depth across all containers. Add up all the measurements. Divide by the number of containers. This is your average. Look for the lowest measurement and the highest measurement. The difference between lowest and highest is your variation.

Step 4: Calculate Your Watering Rate

If the average depth across all containers in 15 minutes is 0.25 inches, your watering rate is 1 inch per hour. Multiply by 4 to get the hourly rate. 0.25 inches in 15 minutes times 4 equals 1 inch per hour.

Now you know how long to run that zone to deliver 1 inch of water. If your rate is 1 inch per hour, run the zone for 1 hour total per week. Split into 2 sessions of 30 minutes or 3 sessions of 20 minutes.

Step 5: Analyze the Coverage Pattern

This is the most important step. Look at your sketch with the measurements marked. Every container should have roughly the same amount of water. A good system has less than 20 percent variation between the highest and lowest container.

If some containers have much more water than others, you have coverage problems. Containers with very little water indicate dry spots. These are the areas that will brown out first in hot weather. Containers with much more water indicate overwatering. These areas may develop fungus or moss.

Common patterns: Low readings between two heads mean the heads are spaced too far apart. High readings near heads and low readings between them mean poor overlap. Low readings at the edges mean poor edge coverage or spray blocked by obstacles. One side consistently lower than the other means a pressure issue or a tilted head.

Step 6: Fix the Problems You Find

Dry spots between heads: Move heads closer together. Or adjust nozzles for a wider spray pattern. Or increase run time on that zone.

Overwatered spots near heads: Reduce the spray distance on nearby heads. Or replace nozzles with lower flow rate versions.

Poor edge coverage: Adjust the arc on edge heads to spray more toward the edge. Or add a head at the edge if the current layout cannot reach.

Tilted spray pattern: Dig up the tilted head. Adjust the swing joint to make it vertical. A head tilted even 10 degrees sprays much shorter on one side.

Pressure problem: If coverage is weak across the entire zone, you may have too many heads on the zone. Remove one head or split the zone. Or check for a partially closed valve or a kink in the supply line.

Step 7: Retest After Fixes

After making adjustments, test the zone again. Run the same 15-minute test with containers in the same positions. Compare the new measurements to the old ones. Coverage should be more even. Variation should be lower. Keep adjusting and retesting until every container is within 20 percent of the average.

This process takes a couple of hours the first time. But once your system is dialed in, you only need to retest once a year or when you notice dry spots developing.

Pro Tips for Accurate Testing

Test in the early morning when wind is calmest. Do not test right after mowing. Freshly cut grass can deflect spray. Do not test when the ground is already wet. Runoff skews the results. If your system has a rain sensor, bypass it for the test. Test each zone separately. Mark the sprinkler head locations on your sketch for reference.

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