Xeriscape is NOT native plants only. Although there is a vast array of wonderful regional native plants, introduced plants that are well-adapted to our climate are a wonderful addition to our native flora. Many Iris, Tulips, and even Roses are examples of introduced plants that are well adapted to nonirrigated landscaping in the Rocky Mtns. Xeriscape is NOT just rocks and gravel. Xeriscape is NOT always lawn-less.
Landscaping is the first thing to consider when water becomes scarce.
Just group together plants of similar water needs and don't over water the groups. Keep it simple. Consider the following four landscape watering zones. Experiment to determine exactly how much and how often to water. This avoids unnecessary delays based on the belief that it's necessary to know exactly how much irrigation is needed before starting.