As one of the most drought-resistant trees in the world, mature olive trees only need an occasional watering during prolonged periods of little rain or drought. Young trees may require up to 2.5 gallons weekly until they are established, depending on levels of rainfall.
While olive trees tolerate a variety of soil conditions, they cannot survive in wet soil, as an overabundance of water in the ground rots the shallow roots. Studies at University of California, Berkeley have determined excessive water to be the leading cause of olive tree death in California. According to SFGate, a drip irrigation system during a drought ensures that the trees have the water they need to produce while limiting soil wetness.