City of San Diego Water Department - Landscape Watering Calculator Drip Irrigation Drip systems can be the most efficient way to irrigate your landscape, using the least amount of water.  There is very little evaporation and no over-spray when the water is placed directly on the soil.  The slow application of water also helps to maintain the air/water balance in the root zone, which promotes optimum growing conditions.  Most drip systems operate at 15 to 30 p.s.i. and can have a uniformity rating of 90 to 95%.  Proper filtration, pressure regulation, and maintenance are essential to good system performance.