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Water Wisely: Auditing Home Lawn Irrigation Systems

Sam Bauer, Extension Educator

A broken sprinkler can waste thousands
of gallons of water in a single year
Auditing irrigation systems is an important practice for maximizing water use efficiency in the home landscape.  Audits entail checking for irrigation uniformity and converting minutes of irrigation to a depth in inches of water applied.   A full irrigation audit should be conducted at least every three years, although proper irrigation requires more frequent monitoring of irrigation system components to ensure that everything is working properly.  Broken sprinkler heads and irrigation of impervious surfaces are very common issues that we observe and these must be repaired in a timely manner. 

Basic Irrigation Auditing Procedure

Step 1: System inspection
Irrigation of impervious surfaces is
bad practice and will cost you money
Run each irrigation zone.  Look for broken sprinklers, low water pressure and arcs or angles of water spray that are distributing water where it is not needed (i.e. on streets or driveways).  Replace sprinklers, correct water pressure issues, and make adjustments to the water distribution so your system is supplying water where it is needed.  

Step 2: Performance testing
Performance testing involves placing catch cans on the lawn in an evenly spaced grid pattern throughout an individual irrigation zone.  Cans should be placed 5 to 8 feet apart for small area spray-sprinklers and 10 to 20 feet apart for large area rotor-type sprinklers.  A minimum of 20 cans should be used for each irrigation zone- more cans allow for greater accuracy.  Tuna or coffee cans work great for this, or you can purchase special catch cans designed for irrigation audits from big box stores for less than $1/each (be sure to use cans that have straight sides). 
Catch cans will allow you to measure
uniformity and rate of irrigation

After the catch cans are placed throughout an irrigation zone, run the zone for a set amount of time; minimum run time should be 30 minutes, but longer run times such as 60 minutes will be more accurate.  Next, measure and record the depth in inches of water in each can.  Repeat this procedure for each individual zone of your irrigation system.

Step 3: Uniformity calculations and scheduling zones
To calculate the precipitation rate of each irrigation zone, calculate the average depth of water in the catch cans for one hour of run time.  For example, if the average depth of our 20 cans was 0.75 inches and we ran the zone for 30 minutes, our precipitation rate would be 1.5 inches per hour.  For uniformity calculations, take the average depth of the lowest 25% of cans (in this case the 5 lowest cans) divided by the overall average of all cans.  For example, if the average of our 5 lowest measuring cans is 0.5 inches, divide 0.5 by 0.75 = 0.67 or 67%.  Irrigation systems with lower than 60% uniformity should be adjusted for better uniformity.
Special cans for auditing
make measurements easy

Once you have calculated the precipitation rate for each zone, you can set the run times.  If your goal is to apply 0.5 inches in one irrigation cycle and the precipitation rate is 1.5 inches per hour, set the zone for 20 minutes.    

For more information on auditing irrigation systems, visit the Irrigation Association website.

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