City of San Diego Water Department - Landscape Watering Calculator Application Rate If you have a spray or rotor system in a lawn area, you can perform a simple test to measure the amount of water your system uses by following these steps: 1. Place three or more coffee mugs, or other flat bottom containers, at various places on your lawn. 2. Turn on the sprinklers for 15 minutes. 3. Use a ruler and measure the number of inches of water in each container. 4. Find the average number of inches in all the containers, and multiply that number by four. This is the number of "inches per hour" that your system delivers. 5. Enter the "inches per hour" number in the box where you are asked for your application rate.