Also remember that a lack of moisture may not directly kill your tree but still ultimately can cause a tree's death. The tree might survive the loss of water only to be ravaged by disease and insects that take advantage of moisture related weakness. Major pine beetle outbreaks are known to occur during the lowering of resistance of a stressed forest of southern and western pine trees.
Trees can be watered with a soaker hose or sprinkler. A soaker should run on the same spot for one to four hours (or until water run-off occurs) to saturate the soil to the proper depth. A sprinkler should be allowed to run until an inch of water can be measured in a cup or water gauge. If you are restricted to hand watering, you can construct a small basin around each shrub, fill it with water, and allow the water to seep into the soil.
If the soil is properly saturated, you will not need to return to water the same area for two or three weeks. Crape myrtles, lilacs, smoke trees, junipers, boxwood, and yews are some of the most drought tolerant shrubs. Azaleas, rhododendrons, witch hazels, Japanese holly, and hybrid tea roses need extra water when weather is dry.
Again, be sure to use a rake to rough up the mulch so the water can penetrate through it. Excessively dry mulch is repellent to water so I suggest you use proper mulching techniques.