Everyone wants to save water, except possibly those who live at the edge of a bog. Here are a few tips:
Drench the soil completely whenever you water, then let it dry out until only the deepest roots are hydrated. That encourages even deeper rooting. Of course, you have to dig a bit to find out how deep your water's gone and even after years of experience I find myself overly optimistic.
New plants need lots of water, even if they've been billed as drought-tolerant. The roots have been confined in a small space and they'll run out of water faster than you may realize.
When trees, shrubs and perennials have settled in for a couple years, water a few times as the leaves are expanding, probably in April and May. We do have dry spells in the Northwest, even in spring, and this is when they need it most. Late summer and into fall is the time to let them dry out. That may even help them get ready for winter. In fact, you'll probably be surprised at how little water most established plants need.