In general, these trees are very drought tolerant. That said, they still need water.  If you have a new little olive tree, water it once a week for the first year. If you have dry air in the house or notice that the top 2 inches of soil is dry, go ahead and water it. Once the tree has taken root and is established, you only need to deep water it once a month. Most importantly, the pot needs to have drainage holes.