City of San Diego Water Department - Landscape Watering Calculator Type of Watering System Each watering system performs differently depending on the types of sprinklers, water pressure, and system design. The Calculator allows you to select the most common types of irrigation systems and uses average values for each system. For example, when you select "sprinkler" on the Landscape Watering Calculator, a default number is used in a mathematical formula to create your custom watering schedule.