Water is one of the most important factors to consider in designing your landscape--its sources and locations will aid you in the placement of plantings of your landscape design. The natural amount of water in your zone also largely affects which plants to choose; a large water supply will allow you to grow plants that are not the hardiest in your landscape environment. Water conservation is a huge part of responsible landscaping.
As you are probably familiar with, a heavy spate of rain does not relieve a drought as well as a slow and steady downfall. Too much water too quickly runs of dry parts of the ground both in a large landscape and in your particular landscape, so remember to give your earth an elongated sprinkle. Considering when you water is another part of becoming a responsible landscaper. Early morning water is the most effective for conservation as the water soaks in rather than evaporates in midday sun. Watering at night precludes the possibility of midday evaporation, but doesn't allow for day light and breeze to air out the wet landscape.
If your climate is naturally hot and dry you will need to apply a more global landscape design, such as xeriscaping in which drought resistant plants are grouped and thirsty ground covers like grass are eliminated from the landscape design and replaced with mulch or garden stones.