How can I tell if there is a problem with my irrigation system?

First, you need to know how much water is required by your landscape. To do this, there is an important term to understand.

Evapotranspiration (ET)

ET is a measurement of passive water loss from soil by evaporation and active water removal by the plant community (transpiration).  ET provides accurate and reliable information as to plant water usage. It will tell you exactly how much water is needed by your residential or commercial landscape.

Base ET can be calculated using

  • temperature
  • wind
  • humidity
  • solar radiation

Conventional Controllers

ET varies tremendously, day to day, and month to month every year with the peak demand for water occurring sometime in mid-summer.

Daily ET Rates Current Standard Program

Daily ET Rates
Current Standard Program

Most irrigation controllers are set to run in the spring on a peak demand schedule because they will receive little if any scheduling adjustments during the growing season.

Peak ET Demand Current Standard Program

Peak ET Demand
Current Standard Program

The blue area shown below depicts why many systems in operation today are applying from 15 – 70% more water than is needed.

Set it and Forget It? Current Standard Program

Set it and Forget It?
Current Standard Program

System Efficiency

Other than my controller programming, how can I tell if my system is operating as efficiently as possible?

First, there are a couple of important terms to understand.

Distribution Uniformity (DU)
In irrigation, Distribution Uniformity is a measure of how uniformly water is applied to the area being watered, expressed as a percentage.


This densogram visually depicts what happens with any zone in an irrigation system. Notice the darker and lighter shaded areas within the zone. These demonstrate how water is being applied at different rates within the zone. No irrigation zone (or even natural rainfall) is completely uniform. Consequently we must irrigate at a rate that will distribute the desired amount of water to the most inefficient area within the zone.

Distribution Uniformity Why is it important?

Distribution Uniformity
Why is it important?

This table dramatically demonstrates what happens when the DU of a zone falls below acceptable operating parameters (generally 65% or higher). At lower than acceptable DU’s, excessive amounts of water must be applied in order to get the desired amount to the driest area or lightest shaded area in the densogram.

Precipitation Rate (PR)
In irrigation, Precipitation Rate is the depth of water applied to the soil per unit of time (in/hr, mm/hr).
Precipitation Rate

Precipitation Rate
Sample rotor manufacturer performance data

All manufacturers provide precipitation rate data for their product. This data (usually developed under lab conditions) may or may not correspond to what is happening in the field with your system.

The best way to determine whether there are any problems with your system is to have a Landscape Irrigation Audit completed by a certified professional. The audit will define any corrections that are required for your system to function efficiently. The audit will also determine the DU (Distribution Uniformity) and the PR (Precipitation Rate) per zone along with all of the other relevant information such as sprinkler efficiency, soil type, plant type, micro-zone, slope percentage, and sprinkler location that are necessary to properly program your controller.