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Irrigation Audit Application User Guide


The purpose of this application is to simplify irrigation auditing and make it possible for any field worker or homeowner, anywhere in the world, to put a basic, water-conserving schedule into a sprinkler controller. Our expectation is that, by removing the computations, novices and experts alike will be able to focus more fully on the practice of applying effective water management strategies. The underlying methodology for calculating this basic schedule is based on the principles in the Irrigation Association's handbook, Landscape Irrigation Auditor, 3rd Edition.

Steps for Effective Water Budgeting

1. Fix obvious problems in the system

It is impractical to calculate an efficient sprinkler schedule for a poorly maintained system. Fix the basic system problems first. Common maintenance problems include:

  • sprinkler heads that do not turn due to wear
  • sprinkler heads that are misaligned
  • broken or missing sprinkler heads
  • leaking sprinkler heads and pipe connections
  • sprinkler heads bent at an angle
  • sprinkler heads that do not rise above the grass
  • sprinkler heads that do not pop because grass has grown over them
  • sprinkler heads with missing or clogged nozzles
  • pressure problems indicated by misting (high pressure) or weak spray (low pressure)

Run each station for 2-3 minutes, observe any obvious sprinkler problems, and fix them. Maintain the system every year at system start, and then make periodic checks during the season.

2. Find and solve the biggest problem areas in each zone

In a well-designed system, just one or two sprinkler heads often create the majority of problems that lead to overwatering. Catch cups with little or no water in them indicate the biggest problem areas, since runtimes or intervals are often increased to compensate for these "hot spots" that get too little water.

Run a pre-audit catch cup test for each station, long enough to get an average of about 10ml in each cup. Where sprinkler heads from different stations water the same area (overlap), make sure to keep the cups in place and run both zones. Then identify cups that are significantly higher or lower than the average. Identify solutions to increase or decrease the amount of water reaching these cups. Possible solutions include:

  • ensure equipment is functioning properly (see Step 1)
  • adjust arc or radius
  • exchange nozzle

Rerun the pre-audit catch cup test and verify that the solutions removed the outliers. The test for "hot spots" should be done every year at system start. It can be combined with Step 1 above to save time. These first two steps will ensure that you are scheduling a well-balanced, high-uniformity system.

3. Conduct the timed catch cup test

Before you conduct a timed catch cup test, make sure you have fixed the obvious sprinkler head problems and removed the "hot spots" in each zone. Run each station long enough to get at least 20ml in each cup. Record the test runtime. Make sure to keep the catch cups in place on overlapping zones (where sprinkler heads of the same type from two zones spray onto the same area) and run each station for the same amount of time. If you are watering each station for 10 minutes, then the test runtime for each zone should be 10 minutes, not 20 minutes. See the Catch Cup Instructions for details on how to set up the cups.

On a well-maintained system you only need to perform the timed catch cup test once, unless there are major equipment changes to a zone or significant changes in system pressure. While it is possible to save time by using the test data from one spray zone as a surrogate for all the other spray zones ("linking"), sprinkler spacing and equipment differences, although imperceptible to your eye, could drive significant differences in precipitation between the zones. Unless you are sure that the zones are homogeneous, it is best to spend a little extra time and test each zone individually. It may take an extra hour or two, but will potentially save significant amounts of water over the life of the system.

4. Group similar zones into hydrozones

Hydrozones are groups of zones which have similar water requirements. Each hydrozone comprises plants with similar water requirements, in similar soil, receiving similar amounts of sunlight each day. Different hydrozones generate very different watering schedules. In a peak ET month, sandy loam might require a one-day interval, while clay loam might only require a three-day interval. Similarly, in a high ET month, dense, cool-season turfgrass might have an ETLof 5.0 inches, while sparse groundcover might have an ET of just 3.5 inches. The key is to schedule watering like things together wherever possible, using separate programs for each group; input each hydrozone into the Irrigation Audit Application separate from the other hydrozones. The number of programs on a controller will dictate the maximum number of hydrozones. Typically you should reserve one of the programs for drip, which has its own, unique scheduling requirements.

5. Input the data into the Irrigation Audit Application

The Irrigation Audit Application requires information for just nine different fields, and only four require any particular effort on the part of the user. The nine fields are:

  • zip or city
  • controller and program name
  • soil type
  • landscape factor
  • root zone depth
  • watering days
  • station name
  • test runtime
  • catch cup volume

Zip or City

The Zip or City Database contains reference data for all US zip codes and Canadian postal codes, as well as virtually all cities and towns in the world. So far we have confirmed that Tristan da Cunha is missing from our database; there must surely be others, and we welcome you to mention any you find. When inputting the city name, it is helpful to add the country name to ensure accuracy. Examples include:

  • 84010
  • Los Angeles, CA
  • Frankfurt, Germany
  • Melbourne, Australia

After you input the zip code or city name and click to another field, the ETo data will automatically populate. For users in remote parts of the world, we recommend that you verify this ETo data with a local university. While we are quite confident in the integrity of our database, we recognize that with a global landmass of 57.3 million square miles, it is quite possible we could have an error or gap in the data somewhere.

Controller and Program Name

This field allows you to designate which controller you are creating a program for and to specify which program that is. Remember that the program should include all stations associated with a specific hydrozone (same plant type, soil type, sunlight exposure). Since many controllers only have two or three programs, you may have to combine some hydrozones, but be sure that the water needs of each aren't too different. You can put whatever you want in this field. If you only have one timer, you might just type: "Program A" (programs are usually designated A, B, C, etc.).

Soil Type

The texture and structure of a soil determine how fast the soil can take water into it without runoff and how much water the soil can hold. While it is possible to get very precise about the texture of a soil, for irrigation scheduling it is useful to use five general classifications: sand, sandy loam, clay loam, and clay. Sand is composed of coarse particles; clay is composed of very fine particles; and the three loam classes are composed of a combination of fine and coarse particles. Unless a soil is truly sand (i.e., water runs right through it) or clay (i.e., it becomes extremely hard and cracks when dry), it is typically best to stick with sandy loam, loam, or the clay loam designation. The following images provide a visual reference for different soil types:

For more precise designation of soil type, particularly if you would like a full soil analysis and fertilization recommendation, send a sample(s) to your local University Co-op Extension. The following table provides the basic characteristics of soil texture classes. (You do not need to know what any of these numbers mean; the application uses them all behind the scenes.):

Soil Characteristics
Soil TypeAvailable Water (Inches/Inch)Basic Intake Rate (Inches/Hour)Max Allowable Depletion (%)
Clay Loam0.160.2550
Sandy Loam0.090.4550
Landscape Factor

The reference evapotranspiration (ETo) value is for a specific grass type, with specific height, density, and sun exposure. The actual conditions in your hydrozones may vary widely. Warm season grasses (e.g., Bermuda, centipede, St. Augustine, bahia, and zoysia) have water requirements which are different from cool season grasses (e.g., Kentucky bluegrass, perennial ryegrass, tall fescue and fine fescue). Some zones will be in full sun while others will be in partial or full shade. Some zones will have a mix of grasses, trees, shrubs, or flowerbeds. As the landscape matures, the initial landscape factor for a particular zone may change considerably as plants fill out, roots extend, and shaded areas increase. This makes it important to reassess this factor from time to time. The following table provides a helpful reference for plant factors which should be used in calculating the landscape evapotranspiration requirement (ETL):

Plant Factors
Plant TypeMaximum AppearanceAcceptable AppearanceLean-Green Appearance
Cool Season Turf0.80-0.850.70-0.750.60-0.65
Warm Season Turf0.70-0.750.60-0.650.50-0.55
Ground Cover0.70-0.800.50-0.600.30-0.40
Mix of Above0.90-1.000.75-0.800.50-0.55
Desert Plants0.40-0.450.30-0.350.20-0.25
Catch Cup Size

Catch cups come in a variety of different sizes. Hydro-Rain and Cal-Poly cups both have 16.25 square inch throat areas. Other brands of catch cups typically indicate the throat area on the side of the cup.

Root Zone Depth

The root zone is the depth or volume of soil from which plants extract water. Typically this is the depth of soil containing 80 percent of the plant roots. A typical target effective root zone for cool season turf grass is 6 inches. The following table shows potential effective rooting depths for different types plants:

Guide to Effective Root Zone Depths
Plant TypeMinimum Depth (in)Maximum Depth (in)
Cool Season Turf48
Warm Season Turf612
Ground Cover46
Reference Evapotranspiration (ETo)

Reference evapotranspiration (ETo) is the sum loss of water from the soil both by evaporation from the soil surface and by transpiration from the leaves of the plants growing on it. It is specific for cool season grass, 4-6 inches in height under controlled conditions. Unseasonal weather patterns may increase or decrease the actual required ETofor any period of time.

Watering Days

Irrigation Audit Application uses the maximum allowable depletion of the particular soil type for a hydrozone and the landscape evapotranspiration (ETL) requirement to determine how often to water. This ensures that enough water is available in the effective root zone to sustain the plants. If you leave the watering days field blank, the system will use this soil moisture logic to specify the frequency of watering. However, many water districts and cities impose restrictions on how often customers can water. If this is the case for your specific site, select the allowed watering days (specific days of the week or odd/even days) and the application will adjust the runtime per day to provide the correct ETLrequirement for the week. This will typically result in more cycles and longer overall system runtimes, especially in high ETLmonths. The actual total amount of water applied for a full month will be the same whether the soil moisture method or watering days method is used; the amount of water per day will, of course, be different.

Station Name

Use this field to identify the name of the station or zone. Examples are:

  • Station 1
  • Zone 5
  • Front Parkstrip
  • Back Rotors

Test Runtime

The test runtime is the length of time, in minutes, that you run the catch cup test for each zone. Make sure to keep the catch cups in place on overlapping zones (where sprinkler heads of the same type from two zones spray onto the same area) and run each station for the same amount of time. If you are watering each station for 10 minutes, then the test runtime for each zone should be 10 minutes, not 20 minutes. You typically only need to run a test long enough to get an average of 20ml in each cup, but it is very important to be precise in recording how many minutes the test lasted.

Catch Cup Volumes

Record the volume contained in each catch cup in a particular zone. You do not have to input the data in any specific order. The application will automatically sort the cup data to do all of the calculations necessary for the watering schedule. Make sure that you input the data in milliliters and do not include decimals (we are not sure how you would get that precise anyway!).

Calculate and Output

After inputting all catch cup volumes, click the calculate button. The output will show the general system and hydrozone parameters; the distribution uniformity for each zone; and the recommended cycles (number of start times), interval (how often) and runtimes (how long) for each station. To see the detailed audit information for a specific zone, click on the name of the zone. The delay between cycles (start times) feature allows you to see how long it will take the program to run through one cycle of all stations. Most controllers "stack" start times, so you could also set all start times the same and the program would run through all stations in order, and then run through the next cycle and so on. Note that, together with the runtimes, you will see a budget percentage. This allows each station to have a constant runtime throughout the year, as the budget reduces runtimes up or down to produce a precise watering schedule with minimal input on your part.

Enter the budget number in the "Budget" or "Seasonal Adjustment" setting of your controller. Each program will have a unique budget percentage. The email out option allows you to send the schedule to yourself. At the beginning of each month the controller will send you an email reminder of the schedule specific to that month. Following these reminders is the key to achieving the best water management possible. If you need to change settings, or if you wish to unsubscribe for a particular watering schedule, click on the associated links in any email for that program.

6. Stay consistent over time

The Irrigation Audit Application produces reliable watering schedules over time, typically within 5-10% of the ETovalues based on "real time" atmospheric data. It is worth noting that "actual" ET can only be determined under very specific field lab conditions for a specific crop. Smart sprinkler controllers simply use real-time (or near real time) weather data to estimate ET for a period. Over a long period of time, water usage based on the Irrigation Audit Application compared with water usage based on a smart sprinkler controller will be very similar.

When using a traditional sprinkler controller, the best practice is to implement an Irrigation Audit Application recommended program and then observe the performance of zones in that program over a period of a few weeks. If a hydrozone (multiple zones) shows signs of too little or too much water, then rerun the audit calculation with an adjusted landscape factor: up for underwatering or down for overwatering. If one of the zones is showing signs of stress, then evaluate whether the landscape factor for that particular zone is different than the factor for other zones. If they are relatively similar, then adjust the runtime for that specific zone: up for underwatering or down for overwatering. During an unseasonably hot or cool period, increase the budget up or down 10% to compensate for the higher or lower ET requirements. ET-based controllers perform this function automatically; with non-ET controllers it is impractical to make such frequent adjustments, so it is best to stay consistent and limit adjustments to implementing the new monthly schedule at the beginning of each month.


We hope you will find the Irrigation Audit Application simple and effective in guiding your efforts to implement an effective landscape water management plan. We welcome your feedback on any aspect of the application.