Watering Calculator

Many of us overwater our plants and lawns. With the assistance of a Water Calculator and Index, you can figure out how much water your lawn and garden really need. If you have an irrigation controller (a.k.a sprinkler timer or clock) that supports the “percent adjust,” seasonal adjust, water budget, or similar feature you can take advantage of this program. This may not be for you if you have a self-adjusting weather-based smart timer.


water budget sprinkler

Use the watering index or CSANS notification to change the percentage each day, week, or month to adjust your watering based on weather to ensure that you are not overwatering your plants and/or lawn!

Step 1: Get started by clicking the link below to create a customized watering schedule using the Watering Calculator. This will help set a baseline for the maximum watering times based on your plant palette, soil type, irrigation system, and geographic location. This schedule corresponds to the maximum outdoor watering required for each month, which is 100% on the “water budget” feature on your sprinkler timer.

Click here to use the watering calculator. Please note: This calculator provides a baseline for the maximum run times and start times. In order to use the watering calculator to create an appropriate watering schedule, the Watering Index (Step 2) must be used to adjust your watering based on weather and changes in plant water needs throughout the year.

Step 2: Use the Watering Index (select weekly or monthly options based on how frequently you would like to modify your sprinkler settings) to adjust your schedule based on current weather patterns. Enter the watering index (for example, 50% weekly or 62% monthly) that corresponds to the frequency in which you choose to adjust your sprinkler timer. To receive up-to-date notifications on the watering index, sign up for monthly or weekly email reminders through the California Sprinkler Adjustment Notification System (CSANS) website here: https://csans.net/.

This will help ensure that your plants are as healthy as possible, and this could save you hundreds and even thousands of gallons a month. Remember, overwatering can be more harmful to your plants and lawn than under watering.

What is a Watering Index?

The Watering Index is a percentage that is calculated from scientific data and used to establish a recommended setting for the water budget adjustment feature. The Watering Index reports three percentages:

Daily: based on conditions the previous day
Weekly: based on average conditions over the previous 7 days
Monthly: based on average conditions over the previous 30 days

The index is normally 100 percent for the hottest time of the year in Southern California – much of July and August. Over the course of the year the Watering Index changes to reflect the landscape’s changing need for water as climatic conditions change. As new Watering Index values are published, the controller’s water budget adjustment feature should be changed to match the current Watering Index value.  The watering times for all valves controlled by one landscape controller will change by the same percentage when the water budget adjustment feature settings are changed.